Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Ed_Chambley on April 07, 2012, 10:57:54 pm
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I just completed a 18 watt preamp with cathode bias El-34's. I checked with a bulb limiter. everything ok, even played a little with it. Everything seemed ok, so went to full power to begin checking voltages. The rectifier tube got hot and flashed and popped the relay ( I use 2 amp relays as opposed to fuses). The tube was very hot. I pulled all the tubes and checked the rectifier voltages and I get 315vac on the reds and 5 vac on the yellows. Put the rectifier back, same thing happened. Tried a few different tubes, same thing. What would be the next step in troubleshooting, I cannot get any voltages without the rectifier.
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I suppose you are using fixed bias.
Check that the bias circuit is working correctly e.g. by measuring the negative voltage on power tubes (pin 5).
/Leevi
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The flashing and popping sound as if something is shorting across the socket for your tube. Maybe something almost making contact, needs the full juice to jump the gap? :dontknow:
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How much B+ voltage do you get with the rectifier tube in? Tried another rectifier? Does the amp work at all? Got a schematic? Got some pics?
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The B+ at pin 8 rectifier tube using a 5u4gb is 315vac and of course at the standby switch. It is not fixed, it is cathode bias. Just as soon as you filp the standby it makes a deep buzzing sound. This is with only the rectifier tube in. I have tried many different tubes. This is the amp where I used a 18watt preamp and a Chiefton Power Section. The tube flashes inside and I see no arching across the socket. I will get some photos later, I ain't much with a digital camera.
I am getting 320 on both reds, 320 on pin2 and 315 on pin 8 (vac). In cathode bias I do not understand where the amp gets its DC other than filter caps. C1 and C2 are a dual 50uf/500v and I have a choke connected across. Hammond 194, a hefty choke.
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Pin 2&8 should be showing DC voltage, not AC. You have AC going into the tube, but DC coming out. At pin 8 you should be showing ~ 385 vdc.
Hate to ask a dumb question, but you do have the red wires going to 4 and 6, and the yellows to 2 and 8, right? Oh, and the CT is grounded?
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In cathode bias I do not understand where the amp gets its DC other than filter caps.
The rectifier tube, 5U4 in this case is a dual diode tube. This is where the AC coming in is changed/rectified to DC going out.
Pin 8 should have DC on it. But to get a stable dcv on it you need a filter cap on it too. 20uF or more would be fine.
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Some Photos. I know I should have vdc on pin 8. here is a photo or 2. Also it is center tapped. I may need to add a cap.
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More Photos
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Couple more
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I used this layout and substituted the octal sockets. If I add a cap, how should I place it? Should it be between standby and pin 8?
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Sorry if this was mentioned.... Have you tried this with only the rectifier tube and the B+ wire from pin 8 disconnected from the rest of the circuit?
How much B+ filtering do you have on that first node?
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Sorry if this was mentioned.... Have you tried this with only the rectifier tube and the B+ wire from pin 8 disconnected from the rest of the circuit?
How much B+ filtering do you have on that first node?
I am not sure what you are suggesting. If I do understand, I have disconnected the b+ from pin 8, but this disables the B+ entirely. Going from pin 8 to standby to the left side of a dual cap can which feeds the OT, a choke connects the other side of the dual cap can which then feeds what I would consider the first node.
I now have a new problem. Now I have a dead short somewhere. This is very weird. When I firest fired it up with the bulb limiter, I played the amp for 5 minutes or so. Nothing got hot. When I went to full power, the rectifier tube flashed and blew the fuse. Now if I reconnect it to the bulb limiter with a known good rec tube, it shines bright off standby. I thought I should get dc current from the cap can, but not so. I can hook up another cap from ground and hoook a wire to pin 8 and get 297dvc. Just cannot figure out the problem. Should I move the choke as it connects the dual cap can together.
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When I went to full power, the rectifier tube flashed and blew the fuse. Now if I reconnect it to the bulb limiter with a known good rec tube, it shines bright off standby.
Yes a direct short, that's why the bulb is glowing.
Ed, divide and conquer.
You might have killed the HT on the PT. Try taking an acv reading from the 2 red PT wires with out the rec. tube pluged in. If good then try just hooking up and powering up just the PT, HT, 5U4, and 1 filter cap, no _ other _ tubes/no B+ current draw. Forget the choke for now and all else down stream in the B+.
Try it with the limiter first and then if it's OK try it with out the limiter, if OK, then try adding the choke, and so forth.
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When I went to full power, the rectifier tube flashed and blew the fuse. Now if I reconnect it to the bulb limiter with a known good rec tube, it shines bright off standby.
Yes a direct short, that's why the bulb is glowing.
Ed, divide and conquer.
You might have killed the HT on the PT. Try taking an acv reading from the 2 red PT wires with out the rec. tube pluged in. If good then try just hooking up and powering up just the PT, HT, 5U4, and 1 filter cap, no _ other _ tubes/no B+ current draw. Forget the choke for now and all else down stream in the B+.
Try it with the limiter first and then if it's OK try it with out the limiter, if OK, then try adding the choke, and so forth.
That is exactly what I am doing now. Good news. PT all good. I am calling it quits for tonight, but the Dual cap is leaking and I did get a spark from the ground post. I built this out of parts I had laying around. The only "new" part is the 50/50 FT dual cap. I have 320vac from both reds and 5.8 no tube. Heaters read good as well. Hooked up a single 100uf/475 to ground and ran a wire back to pin 8 and got a reading of 295vdc. Tomorrow I will hook it to one side of the dual and we will see.
Thanks for the guidance.
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Use your eyes and your ohm meter to find the short on the B+ rail.
Your board appears to be supported by only two 1/4x20 bolts on the tube side? Is there any support on the pot side? How high does the board sit above the chassis?
There's a lot of plastic coated solid wire in this amp. Is that low voltage control wire from a thermostat or sprinkler system, or similar application?
( I use 2 amp relays as opposed to fuses).
Are you sure?
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Quote:"Also it is center tapped."
Hope you didn't ground the rectifier center tap!!!
Spend some time and clean up your wiring mess.It will save you lots of time when troubleshooting a problem in the future.
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Use your eyes and your ohm meter to find the short on the B+ rail.
Your board appears to be supported by only two 1/4x20 bolts on the tube side? Is there any support on the pot side? How high does the board sit above the chassis?
There's a lot of plastic coated solid wire in this amp. Is that low voltage control wire from a thermostat or sprinkler system, or similar application?
( I use 2 amp relays as opposed to fuses).
Are you sure?
The wire is pvc, 20ga solid core copper. Not low voltage, but how could that cause a dead short? Current leaking out of the jacket. The 2 amp relay states 2 amp. I get them from weber. I have them in a few builds. I like them, but I can put a fuse holder in just as easily, the hole is drilled large enough.
There is support on the tube side, you cannot see it, but there is a board cut off the same material mounted with epoxy to the chassis. It gives me enough room to run the wires under with plenty of wiggle room. The board is 1/4" from the chassis.
Problem with using eyes and meter, I get no reading at the first filter cap and I cannot understand why. It is a straight shot from pin 8 when I bypassed the standby switch. I am assuming the short is there, but I have not checked it. I have a farad meter and will check it shortly.
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Quote:"Also it is center tapped."
Hope you didn't ground the rectifier center tap!!!
Spend some time and clean up your wiring mess.It will save you lots of time when troubleshooting a problem in the future.
It is a very small chassis. The wiring is pretty direct. Suggestion of how to clean it up? The board runs from end to end of the chassis, so the option of making pretty tie-downs around the board weren't very feasible.
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Not low voltage, but how could that cause a dead short?
The insulation burns up easily with a soldering iron, exposing bare wire. Just an observation. Probably not related to your problem.
The 2 amp relay states 2 amp. I get them from weber.
It's a circuit breaker, not a relay.
The board is 1/4" from the chassis.
Dangerously close to the solder lugs on that dual cap can!
I am assuming the short is there, but I have not checked it. I have a farad meter and will check it shortly.
Why haven't you checked it? Farad meter is useless in finding a short circuit. Use your eyes and your OHM METER. You should find it in 5 minutes.
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Not low voltage, but how could that cause a dead short?
The insulation burns up easily with a soldering iron, exposing bare wire. Just an observation. Probably not related to your problem.
The 2 amp relay states 2 amp. I get them from weber.
It's a circuit breaker, not a relay.
The board is 1/4" from the chassis.
Dangerously close to the solder lugs on that dual cap can!
I am assuming the short is there, but I have not checked it. I have a farad meter and will check it shortly.
Why haven't you checked it? Farad meter is useless in finding a short circuit. Use your eyes and your OHM METER. You should find it in 5 minutes.
Correction, I have a circuit breaker.
I have traced everything. I now have a diode socket in the rectifier. Lots cheaper than my nice tubes. I have 438vdc at pin 8. On the other side of the cap can I have 386vdc. Everything is hooked up except the OT. The OT is causing the short which I did not expect as it worked at first.
Initially, I did use a meter to check the cap and got nothing. Now I've got one red wire when I hook it to the cap, I get the short and a loud humming. Later I am going to check to see if I have it wired correctly to the speaker out. Knowing me, I may have it backwards. Could this cause these symptoms? If so, why did it work then not? Also, the layout shows connecting it to the first side of the dual cap where I have 438vdc. This would be prior to the choke.
I have made a cover for the cap can to isolate it from the chassis and board, I just had it removed for the photos.
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The OT is causing the short which I did not expect as it worked at first.
Follow the short. Leave the OT red lead disconnected. See if you have the short on pins 3 of the output tubes. If so, disconnect the OT leads from the tube sockets. Is the short still on the red lead or is it still on a tube socket?
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The OT is causing the short which I did not expect as it worked at first.
Follow the short. Leave the OT red lead disconnected. See if you have the short on pins 3 of the output tubes. If so, disconnect the OT leads from the tube sockets. Is the short still on the red lead or is it still on a tube socket?
I have no short on pin 3 when connected with red disconnected. No short with pin 3 socket with wires disconnected. ohm readings from b+ connection to brown plate lead 76, blue 82. I read somewhere that if you were in 10's to a few 100's, the windings are good. Over 1 meg, dead OT. Don't know how true this is, but I thought I would check it since I had everything disconnected.
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Is the dangling red OT lead still shorted to chassis with the plate leads disconnected? If so, the OT is bad. If not, something was likely boogered where the red lead connected to the cap can.
We're talking about a short, but there is likely some resistance value. What is that value, even if it is zero ohms?
I have 438vdc at pin 8. On the other side of the cap can I have 386vdc. Everything is hooked up except the OT.
IOW, you have 52 volts dropped across the choke? I'm concerned about that. There is typically only a small voltage dropped across the choke. 52 volt drop means a fairly large current through the screens or else where downstream. However, this may be normal since the plates have no voltage on them.
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Is the dangling red OT lead still shorted to chassis with the plate leads disconnected? If so, the OT is bad. If not, something was likely boogered where the red lead connected to the cap can.
We're talking about a short, but there is likely some resistance value. What is that value, even if it is zero ohms?
I have 438vdc at pin 8. On the other side of the cap can I have 386vdc. Everything is hooked up except the OT.
IOW, you have 52 volts dropped across the choke? I'm concerned about that. There is typically only a small voltage dropped across the choke. 52 volt drop means a fairly large current through the screens or else where downstream. However, this may be normal since the plates have no voltage on them.
I got tired last night. I will disconnect the plate leads again and see if just connecting the red lead causes a short. If so, I understand it is a transformer short. I hate that if it is the case. It is a MM OT. I don't have much money in it, but still. Have you ever tried to repair a shorted winding?
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Follow Sluckey's lead here.It is unlikely the OT is shorted,but you need to follow the steps.
That 52v drop is interesting.Something has to draw that amount of voltage and if there are no tubes to draw current,where is the draw?
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With every wire disconnected from the OT, I get a short when connected to the B+. Bad OT. Contacted Mercury Magnetics today and they told me their transformers are really though and usually don't short before something else breaks. They said ship it to them and they would check to see if it was defective. Probably a waste of time, but I asked if a rewind was cheaper than buying new and they said it was more expensive. This makes no sense unless they are not making them anymore and just selling them. In my mind app the parts other than winding cost something. Seems like rewinding should be cheaper.
The OT is 4900/8ohms. This build is a cathode bias PP el-34 and maybe run kt-66's. If I get another OT I would like the option of multi-taps. Anyone have a suggestion for an OT that will fit this bill.
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You are having some difficulty here I can see,but a rewind is ALWAYS more money cause the labour cost goes up.
You are still missing something cause like MM says they don't short out for no good reason.
It's likely something you are missing which is not hard to do even for a seasoned repair guy.I'd hate to have you get a new OT and have the same issue.
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You are having some difficulty here I can see,but a rewind is ALWAYS more money cause the labour cost goes up.
You are still missing something cause like MM says they don't short out for no good reason.
It's likely something you are missing which is not hard to do even for a seasoned repair guy.I'd hate to have you get a new OT and have the same issue.
I agree, I would hate to buy a new OT and it be something else. The amp was working with the current limiter and sounded good. Somewhat distorted. I wish I had another ot that was not installed in another amp. But what else can explain connecting 1 wire from the ot at c1 or c2 or c3 with all the other wires disconnected and get a short. When I had everything connected, if I touched the red wire to a cap I could hear it pop in the speaker with the tubes in. With no tubes, I get the short.
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Here is the deal. I disconnected the black and green from the speaker out. Short disappeared. I instaled all the tubes. I get 401vdc on both plates of the el34's. Problem is I get -401vdc from the speaker green and the black. Negative. I do not understand this, but it seems like I am getting plate voltage to the speaker out. Any ideas?
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Ed, don't run that OT with out a speaker load or power R of the correct ohms on it. :w2:
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Ed, don't run that OT with out a speaker load or power R of the correct ohms on it. :w2:
I know what you mean. Flyback. It was only disconnected long enough to see the short disappear the I shut down the amp. I have never had a speaker connection shock me before. It bit me a little, so I put a MM on it. I was going back through everything. Checking sockets, voltage. Everytime I disconnected the red, by short disappeared. I have checked the wiring looking for something wrong. There are only 5 wires. Red, blue and black. Black ground and green 8ohms. I cannot find anything incorrect except when I connect the OT. Put a 10 ohm 15 watt resistor. Lamplimiter lit up the room. Psyconoodler suggested more testing. The only thing I know for sure is if I hook up the OT I get a short. With the plate leads disconnected I get 401 vdc on each. I connect them, I get a short and have no B+ at all. Touch the speaker out and get a shock. This aint right. It's like it is hooked up backwards.
What could it be if not the OT? Forgot to mention if I have the speaker wires connected I get no plate voltage. I had then disconnected for about 5 seconds. If that kills an OT, it was ready to go anyway.
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Test the OT. Disconnect all five wires. Use your ohm meter. Put one meter lead on the red OT wire.
1. Put the other meter lead on the blue wire. What is the resistance reading?
2. Put the other meter lead on the brown wire. What is the resistance reading?
3. Put the other meter lead on the green wire. What is the resistance reading?
4. Put the other meter lead on the black wire. What is the resistance reading?
5. Put the other meter lead on the OT shell. What is the resistance reading?
I want 5 meter readings, even if the meter says OL or infinity, or whatever.
Now remove the meter lead from the red OT wire and reconnect to the black OT wire.
6. Put the other meter lead on the blue wire. What is the resistance reading?
7. Put the other meter lead on the brown wire. What is the resistance reading?
8. Put the other meter lead on the red wire. What is the resistance reading?
9. Put the other meter lead on the green wire. What is the resistance reading?
10. Put the other meter lead on the OT shell. What is the resistance reading?
I want 5 more meter readings, even if the meter says OL or infinity, or whatever.
Please answer these ten questions directly. No other info is needed to determine if your OT is faulty.
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Guys you can turn on a tube amp with no load and not worry too much about it blowing up the OT as long as their is no input signal.It's good practice to have a load on it anyway,but it won't blow up if you accidentally forget the speaker.
Ed, MM wiring can be convoluted so make sure one of your plate or even the center tap wire isn't hooked to your speaker jack!!!
Color codes may be different with MM.
If you understood more of how the OT works it would be easy to figure out with just an ohmmeter as Sluckey is showing you.
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Guys you can turn on a tube amp with no load and not worry too much about it blowing up the OT as long as their is no input signal.It's good practice to have a load on it anyway,but it won't blow up if you accidentally forget the speaker.
Ed, MM wiring can be convoluted so make sure one of your plate or even the center tap wire isn't hooked to your speaker jack!!!
Color codes may be different with MM.
If you understood more of how the OT works it would be easy to figure out with just an ohmmeter as Sluckey is showing you.
I did some of the checks he mentioned, I will do the rest and report. I have a hookup diagram from MM It is straightforward. I attached it. Doesn't get much simpler.
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I throw this in because i forgot to ground speaker jacks once. Are your speaker jacks grounded?
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nevermind..looks like old style grounded to chassis as soon as they are bolted in.
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Test the OT. Disconnect all five wires. Use your ohm meter. Put one meter lead on the red OT wire.
1. Put the other meter lead on the blue wire. What is the resistance reading?
2. Put the other meter lead on the brown wire. What is the resistance reading?
3. Put the other meter lead on the green wire. What is the resistance reading?
4. Put the other meter lead on the black wire. What is the resistance reading?
5. Put the other meter lead on the OT shell. What is the resistance reading?
I want 5 meter readings, even if the meter says OL or infinity, or whatever.
Now remove the meter lead from the red OT wire and reconnect to the black OT wire.
6. Put the other meter lead on the blue wire. What is the resistance reading?
7. Put the other meter lead on the brown wire. What is the resistance reading?
8. Put the other meter lead on the red wire. What is the resistance reading?
9. Put the other meter lead on the green wire. What is the resistance reading?
10. Put the other meter lead on the OT shell. What is the resistance reading?
I want 5 more meter readings, even if the meter says OL or infinity, or whatever.
Please answer these ten questions directly. No other info is needed to determine if your OT is faulty.
Since you are asking for a resistance reading to the shell, I should unbolt it from the chassis?
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I would say no, he just wants to see if any of the windings are shorted to the shell and/or to each other.
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Test the OT. Disconnect all five wires. Use your ohm meter. Put one meter lead on the red OT wire.
1. Put the other meter lead on the blue wire. What is the resistance reading?
84.0
2. Put the other meter lead on the brown wire. What is the resistance reading?
75.1
3. Put the other meter lead on the green wire. What is the resistance reading?
78.6
4. Put the other meter lead on the black wire. What is the resistance reading?
78.5
5. Put the other meter lead on the OT shell. What is the resistance reading?
It puts a 1 in the far left, no reading
I want 5 meter readings, even if the meter says OL or infinity, or whatever.
Now remove the meter lead from the red OT wire and reconnect to the black OT wire.
6. Put the other meter lead on the blue wire. What is the resistance reading?
6.3
7. Put the other meter lead on the brown wire. What is the resistance reading?
152.1
8. Put the other meter lead on the red wire. What is the resistance reading?
78.1
9. Put the other meter lead on the green wire. What is the resistance reading?
.9
10. Put the other meter lead on the OT shell. What is the resistance reading?
1 in the left side, no reading
All ohms
I want 5 more meter readings, even if the meter says OL or infinity, or whatever.
Please answer these ten questions directly. No other info is needed to determine if your OT is faulty.
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The OT is bad, shorted between primary and secondary.
This is an uncommon failure, especially for a new transformer. Hopefully MM won't claim you boogered the wiring.
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The OT is bad, shorted between primary and secondary.
This is an uncommon failure, especially for a new transformer. Hopefully MM won't claim you boogered the wiring.
Its not new. I got it in a box of things for 50 bucks. I have used 3 PT out of that box and many parts, so I don't feel so bad. I will send it back, but you know how guarantees on electrical parts are. You got a suggestion on a replacement? EL-34 and maybe KT-66.
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You got a suggestion on a replacement?
Yeah. Buy something from Doug.
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You got a suggestion on a replacement?
Yeah. Buy something from Doug.
I buy most everything from Doug, but this is a different beast. Cathode El34.
Like this one
40 watt 2 6l6 2-4-8 ohm output
Output for Super Reverb, Tweed Bassman, Bassman heads
50 watts with 2, 4 and 8 ohm secondary taps. Great upgrade for Pro Reverb, Bandmasters, etc.
This is the transformer that is being used to make Vibroverb's out of Bandmaster reverb heads.
Note: This transformer is physically larger than a pro reverb or bandmaster output.
If you are upgrading, you will probably have to drill some new mounting holes.
Two 6L6 power tubes
Part number 018343
Or do I really need this much. Problem with Doug's Trans, most are not 8 ohms and most of my cabs are. The Marshall Trans he has $$$$. Are they that good?
I don't think the deluxe will be enough, do you?
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I'd get something advertised for 2 x EL34s, or 3400Ω:4/8/16Ω
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Called Hybour. They are making me one in the same specs as the Chiefton. I would think that will work. Not a bad price. Alden said that transformer was a little on the special side. Mercury quoted $319 for it. $78 shipped from Hybour. They make good stuff and they are very easy to deal with. He said it was actually 3800 ohms and 4-8-16. He explained why it was different. Has something to do with separate resistors and cps for each tube. It was over my head, but there is something else inside the transformer beside simply windings. I forget what he said, but I am sure you know.
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It's 'HEYBOER'
Never heard of anything different,certainly separate resistor/caps don't have anything to do with it.Sounds like a normal transformer for a Marshall to me.
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It's 'HEYBOER'
Never heard of anything different,certainly separate resistor/caps don't have anything to do with it.Sounds like a normal transformer for a Marshall to me.
I will report back when I get it, but he said he has a 3400ohm 4-6-16 which was for marshall's like 800's, but this one is 3800 ohms. Not much different, but there are 2 additional parts inside. I forget, but they shipped it today and invoiced me and I have no account with them. Said I could return it if it did not have the tone I wanted. Risky way of doing business, but I guess they are looking for ways to increase business. I have used many H"E"ybour transformers. Mostly PT's tho, but I have never had a problem with one. Internet rumor is Doug gets his from Heybour. They are not chinese for sure. Shipping weight is over 8lbs. I might put it into a JTM-45 build I bought from someone who built it with cheap parts and use that one in this build since I built this from used parts.
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Got the new OT. It is just a copy of a Drake Plexi. Anyway, got it hooked up and I am having problems. I have 450vdc at c1 and c2 445vdc.
v5
1-0
2-3.7vac
3-445
4-445
5-0
6-445
7-3.7vac
8-0
v4
Same
V3 which is not the PI I am getting no readings except on the heaters
v2 the PI only reading is from the plate resistors 30vdc
v1 nothing
Only tube in place is a ss rectifier.
Any ideas where to look. How can there be so much current on the grids?
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Nevermind! I don't have the resistors in the correct place. :BangHead:
I basically have nothing for dropping resistors. 270 ohm. Looks as if I need 10k on each g1 and at least 2k on each g2.
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I have this hooked up and the results are not good. I am getting low volume on th 8 omn out, little more on the 16 and none on the 4 ohm. Voltage testing.
Recitifier I get 670vac red to red
Pin 8 has dropped to 305vdc. Don't understand this since I had 400 with a tube and 433 with ss.
V5-El34
Pin 1 and 8-0vdc
Pin 3- Switch on Starts at 277 and begins dropping
Pin 5- Starts at 76 and increases as the plate dropps
Same thing with V4-El-34
I have 151 vdc of the plates of the PI which is V2
V1- 115
V3- 132
I am sure I have the power section setup incorrectly. I have never built a cathode bias amp. My questions are can completing the circuit cause that large of a drop in the B+ at the rectifier?
I was using the Chiefton schematic as a guide which I attached earlier. I do not think it is going to work in this case. All I am trying to do is put EL-34 in an 18 watt build.
Anyone have a recommendation of the values of the cathode cap and resistor. The chiefton uses one for each tube and 1k tied to 2, 1k for each pin 5. 10K's to pin 4.
There has to be an easier way!
Anyone have an idea of a simple way to convert this 18 layout to run EL-34. It was just an amp I built out of parts I had laying around, but now I have gone beyond this and have some very nice parts in it.
I do not have any shorts, but the PT is getting hotter than I am comfortable with and also the power tubes which I do not understand.
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There's no reason why you can't run an 18W TMB preamp into the Chieftain power amp. The dividing point is the input to the PI. Use TMB circuit up to the PI input caps. The 4 resistors (grid and cathode, looks like a bird's foot on the TMB layout) need to be Chieftain values since the EL34s have a different drive requirement than the EL84s. Everything from the PI plates to the speaker need to be Chieftain circuit.
Wiring and adapting the Chieftain power supply seems to be giving you a lot of trouble. You'll have to make some subtile changes here, since Matchless is fond of using parallel B+ nodes, rather than the more common series B+ rail. I cannot emphasize how important it is to have a schematic showing exactly how you will accomplish this. Take the time to draw it out. Post the schematic and we'll check it out for you.
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I understand what you are referring to. If I could find an editable schematic of the Ritchie's 18 watt (I have looked) I could put this together in no time. The 470k's have been changed to 220K. The 8k2's from the 18 watt change to 10K. These connect to pin 5 on the EL-34. My cap is dual 50uf/500v. After a choke (40h/50ma-420ohm) connecting C1 to C2 I have a 1k, 10 watt connected to 2 more of the same going to each individual pin 4 of the EL-34.
What is the section BRILL VR5 500KA with the cap .0047uf. It is a pot I assume for Brilliance and I don't know if it is necessary.
Here is where I am lost. The Chiefton Schematic shows 2 individual caps with bypass resistors of 270ohm commonly grounded, negative side. Individual positive leads to pin 8 cathode and looks as if it is commonly connected at pin 1 the suppressor grid.
What I have done is connect the resistors across the caps connecting them to the leads from the negative and positive side of the cap. Common ground on the negative side of the cap (I am thinking this is my mistake) because when grounding, I am grounding both caps and both resistors. Then the leads from the positive side of the cap are commonly connected to pin 1 and 8 of each individual tube..
My question about the Chiefton Schematic here is how should the cathode layout be? I should have dc voltage at the cathode, shouldn't I? The Schematic states 24vdc.
I really do not understand the Chiefton cathode arrangement, but it looks like everything is grounded negative, bypassed at 270 ohms and connected individually to each tube, but common to pin 8 and 1 of each EL-34. Should I connect the resistor to pin 1 and the cap to pin 8 separately?
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The Brilliance pot is the same as the Vox cut pot.
As for the cathodes...
1. Connect pin 1 to pin 8 using a jumper directly on the sockets (V7 and V8). This is a basic EL34 requirement.
2. Connect a 270R between pin 8 and ground of V7.
3. Connect a 250uF cap between pin 8 and ground of V7. Positive lead to pin 8.
4. Connect a 270R between pin 8 and ground of V8.
5. Connect a 250uF cap between pin 8 and ground of V8. Positive lead to pin 8.
Look at the TMB layout. See the parallel cap and resistor on the left end of the board? That's the single resistor/cap for the cathodes. Since you are using individual resistor/cap for each tube, you need to put two more turrets on the board, spaced appropriately to accomodate the extra resistor/cap. If there is not room on your board you'll have to mount them off board.
Look at the attached pic. I've separated the cathode circuits. Is it easier to see what's happening now?
BTW, The pin numbers are wrong on the Chieftain schematic. Pin 8 is really the cathode and pin 1 is really G3.
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The Brilliance pot is the same as the Vox cut pot.
As for the cathodes...
1. Connect pin 1 to pin 8 using a jumper directly on the sockets (V7 and V8). This is a basic EL34 requirement.
2. Connect a 270R between pin 8 and ground of V7.
3. Connect a 250uF cap between pin 8 and ground of V7. Positive lead to pin 8.
4. Connect a 270R between pin 8 and ground of V8.
5. Connect a 250uF cap between pin 8 and ground of V8. Positive lead to pin 8.
Look at the TMB layout. See the parallel cap and resistor on the left end of the board? That's the single resistor/cap for the cathodes. Since you are using individual resistor/cap for each tube, you need to put two more turrets on the board, spaced appropriately to accomodate the extra resistor/cap. If there is not room on your board you'll have to mount them off board.
Look at the attached pic. I've separated the cathode circuits. Is it easier to see what's happening now?
BTW, The pin numbers are wrong on the Chieftain schematic. Pin 8 is really the cathode and pin 1 is really G3.
I am not sure of the uf on the cap, I believe it is 170 but I know it is not 250, problem?
Here is a drawing of what I have done. Let me know where I went wrong.
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Let me know where I went wrong.
QUICK! REMOVE THOSE 1 OHM RESISTORS! NOW!
The Chieftan schematic shows 250uF caps. The caps you're using won't make much difference.
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Let me know where I went wrong.
QUICK! REMOVE THOSE 1 OHM RESISTORS! NOW!
The Chieftan schematic shows 250uF caps. The caps you're using won't make much difference.
So that is the problem, the resistors. Should be ground direct? Or grounded through the cap and resistors. This is bypassing the caps and resistors and taking the cathodes directly to ground. That is why when I power up I get a constant drop in voltages on the grid. What else is it doing? Is this why my pt is getting hot? The amp is working against itself. Why did it not show up on the bulb limiter?
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Argh!!! Forget about grounding the cathode and just wire it like I already explained in verrry great detail!
You know, it's very frustrating that you forgot to mention those 1 ohm resistors. That was a big no-no. Nowhere on your TMB layout or the Chieftan schematic did you see 1 ohm resistors on the output tubes. Those resistors probably cost you an OT. Please, in the future, give all info. And learn how to draw and post a schematic.
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Argh!!! Forget about grounding the cathode and just wire it like I already explained in verrry great detail!
You know, it's very frustrating that you forgot to mention those 1 ohm resistors. That was a big no-no. Nowhere on your TMB layout or the Chieftan schematic did you see 1 ohm resistors on the output tubes. Those resistors probably cost you an OT. Please, in the future, give all info. And learn how to draw and post a schematic.
Steve, Sorry to frustrate you. It is not my intention. You cannot know what you do not know. There are many schematics which do not contain the 1 ohm resistor, but people put them there anyway. I just did not know. If it cost me an OT, that is waaaaay less than the price I have paid learning many other things. I am learning and I appreciate your help. I am also learning how to draw a schematic. I cannot do it all right now, but I do have some of the things in place. The only reason I mentioned the grounding is I am trying to understand what is happening when you do. It seems like you are more than irritated with me currently so I will go for now.
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Well, I am back and the damn thing is awesome. Sounds like an old plexi. A few tone stack changes and a cap change on the normal channel and I got a keeper. Man it is raw wide open and turn the volume knob back about 2 notches and it cleans up like a gentleman. 2, 12's may be a little much for it, but they sure do sound nice. It is one rock and roll machine. I can't thank you guys enough, especially Steve. I know I get the cart before the horse, but I am coming along. While I made many mistakes in my first cathode build, I did learn a lot. To me, that's :wav: :blob10: :occasion14: :m7 what it is all about.
Awesome, Awesome, Thank you, Thank you! Stick a fork in it.
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me too
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So that is the problem, the resistors. Should be ground direct? Or grounded through the cap and resistors. ... What else is it doing? Is this why my pt is getting hot? ... Why did it not show up on the bulb limiter?
The correct connection is Cathode -> 1 ohm -> un-grounded side of cathode resistor/cap -> grounded side of cathode resistor/cap.
So the 1 ohm resistor is in series from the tube's cathode to the bias components. That forces the tube's cathode current to flow through the 1 ohm resistor. It also requires that you either measure the voltage across the 1 ohm resistor with the meter leads on either side of that 1 ohm resistor. That, or you run 2 wires for each 1 ohm resistor to meter jacks, so that you can measure across each 1 ohm resistor.
When you draw that out, you'll notice that 2 of the wires duplicate each other; the ones from the ungrounded side of the cathode resistor. So you can combine those into 1 wire, and simply use 3 wires, 3 jacks.
What the 1 ohm resistors did was provide a parallel path from the cathode to ground. Now, tube current and bias was not detemined by the 270 ohm resistors... instead you had 1 ohm bias resistors! The current took the path of least resistance.
Bias voltage would have measured at almost nothing, because even 1 ampere flowing through 1 ohm only results in 1v dropped across your 1 ohm cathode resistor (slightly less than 1 ohm due to the parallel 270 ohm). Output tubes would be biased near 0v, and tube current goes way up. That makes your PT hot.
Interestingly, it still doesn't show on the lightbulb limiter. A hard short-circuit from B+ to ground would cause very much more than normal current to flow, lighting the bulb brightly. Your situation probably caused double- or triple-current, but not enough to register as a "major fault" and pull enough current to light the bulb brightly. Unfortunately, this was one of those gray-area cases... kinda like pulling enough current to burn up a transformer, but not enough to trip your house's breaker.
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I have a question about tube swaps. Lots of new low power tube amps advertise you can use EL-34, 6l6, 6v6, basically any octal power tube. Doesn't that cause a OT mismatch? Like the OT I got for this amp is a 3k4 which is great for EL-34 or maybe KT88, not sure. But 6v6 likes 6600 to 7000. Is it just advertising crap. I mean everything is different between using different power tubes. What are they doing, just running them mismatched with the OT or is there something I do not understand. Another thing about this build is I disconnected the 4 ohm tap as I have no 4 ohm speakers. There was a noticeable tonal and volume change. How is this possible?
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OK, frustration is gone today. Sorry for losing it yesterday.
Another thing about this build is I disconnected the 4 ohm tap as I have no 4 ohm speakers. There was a noticeable tonal and volume change. How is this possible?
It could not have been wired like the Chieftan schematic. I'm guessing you just connected it to a separate jack similar to the Chieftan schematic? If so, the only possible errors I can think of would be you connected the 4 ohm tap to the ground lug of the jack, or you used a switching jack with the switch jumpered to the ground lug. If you are using separate speaker jacks for each secondary tap, DON'T USE SWITCHING JACKS. (Or if you do, don't connect the switch.) If you wired it some other way, please share. What exactly was the 4 ohm tap connected to?
You still should make the changes to the PI resistors I mentioned earlier. Look at the attached pic...
When you draw that out, you'll notice that 2 of the wires duplicate each other; the ones from the ungrounded side of the cathode resistor. So you can combine those into 1 wire, and simply use 3 wires, 3 jacks.
Don't forget, Ed has separate cathode resistors, not a single shared resistor.
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OK, frustration is gone today. Sorry for losing it yesterday.
Another thing about this build is I disconnected the 4 ohm tap as I have no 4 ohm speakers. There was a noticeable tonal and volume change. How is this possible?
It could not have been wired like the Chieftan schematic. I'm guessing you just connected it to a separate jack similar to the Chieftan schematic? If so, the only possible errors I can think of would be you connected the 4 ohm tap to the ground lug of the jack, or you used a switching jack with the switch jumpered to the ground lug. If you are using separate speaker jacks for each secondary tap, DON'T USE SWITCHING JACKS. (Or if you do, don't connect the switch.) If you wired it some other way, please share. What exactly was the 4 ohm tap connected to?
You still should make the changes to the PI resistors I mentioned earlier. Look at the attached pic...
When you draw that out, you'll notice that 2 of the wires duplicate each other; the ones from the ungrounded side of the cathode resistor. So you can combine those into 1 wire, and simply use 3 wires, 3 jacks.
Don't forget, Ed has separate cathode resistors, not a single shared resistor.
Steve, everyone get frustrated while teaching. I don't take it personally. I will guarantee you it will not be the last time you get frustrated with me. Remember, I asked you what is the best way to learn about this stuff and you said hang around here, read and ask questions. And while I am not at the level of a lot of the others, I will be. I will ask why. Now I understand the 1 ohm resistor became my bias resistor because of the path of least resistance. I did not mention it earlier because I did not know to. In reading in Doug's library about installing the 1 ohm resistor it does not specify this method being only for fixed bias. The mistake I made gave me a great understanding of cathode bias so in my opinion it was of great value.
Now the 4 ohm. I usually use individual Switchcraft 11 jacks with no selector. I run a common through all 3. From left to right looking at the back, 16-8-4. Then I simply connect each wire to the tip. In this case Gray-16 Ohms, Green-8 ohms, Yellow-4 ohms, orange is common. I probably have the tip and ground reversed on the 4 ohm, I will check. There is really nothing else it could be.
Also, I will change the PI resistors as there are some other things I still need to do like installing Negative feedback. I will probably make this switchable as the amp has a really cool sounding grind and does it at a nice volume. The tone stack is in need of tweaking, but this is the last thing I will do before welding up a top cage. Also, I am not too sure of the normal side. I have changed the layout and I only have 1 input for each side as I did not want to use a small pot for the master.
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...things I still need to do like installing Negative feedback.
You do realize that neither the Chieftan nor the 18Watt TMB uses NFB?
Have you considered how you will implement NFB? Both sides of the PI are already in use. You will have to mix the TMB and NOR channels together (Fender style) feeding into one input to the PI. Then you will have a free input to the PI for the NFB loop. It'll be fairly easy and straight forward, but have a plan before you proceed.
I think you have a special design as is. I'd hesitate to put NFB in it.
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It is rather cool. I am going to complete all the other things first. Oddly enough, the volume was unexpected to say the least. I was sort of expecting paint peeling at full throttle, but at about half on the volume knob you reach (master and volume) a very clean max volume. Continue on and it makes this very raw distortion. Sounds like Bad CO or Free using a Les Paul, but the SPL doesn't increase much. Using a tele is entirely something different. I can't quite put my finger on it. I have only ran it through my 2 12's alnico Silver and Blue Webers. I guess what I am thinking is getting a little more control over the tone stack. It is very mid sounding, but 18 watters are. Doesn't mean they have to be that way. Tweaking tone is individual taste anyway. I will say this, I do not own an amp that with such a brown sound that doesn't make you cover your ears until this one.
I was just thinking a Negative Feedback would give me more control, but as I think about it I always run my Super Reverbs with the NFB disconnected and have a great deal of eq.
I will make the changes you suggested and see where I am. This amp is the first one I have ever considered recording sound to post. I am sort of excited about it, but I am sure that is obivous. Like when I was 14 and got my first Marshall Plexi. My father bought it for me. Now I know it was because he did not want me using his 66 Super and I glad he did. The plexi is gone and I now have the super. It looks lke new, just some pitting on the chrome.
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When the rectifier tube shorted, it dumped high VAC onto your filter cap(s) (which they are not designed to cope with), causing one (or more) of them to short to ground, causing the B+ to short to ground. Until you replace the shorted filter cap(s), you will continue to blow fuses.
Your PT(s) may in fact probably still be okay if the mains fuse has been doing its job.
As to what made the rectifier tube short; could be carelessly-soldered socket pins shorting to ground, or it could've just been a bad tube. I always put SS diodes in series between each side of the high tension winding and the respective rectifier tube anode (cathode/banded-end pointing towards the tube's anode) to protect the system from a rectifier tube short
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When the rectifier tube shorted, it dumped high VAC onto your filter cap(s) (which they are not designed to cope with), causing one (or more) of them to short to ground, causing the B+ to short to ground. Until you replace the shorted filter cap(s), you will continue to blow fuses.
Your PT(s) may in fact probably still be okay if the mains fuse has been doing its job.
As to what made the rectifier tube short; could be carelessly-soldered socket pins shorting to ground, or it could've just been a bad tube. I always put SS diodes in series between each side of the high tension winding and the respective rectifier tube anode (cathode/banded-end pointing towards the tube's anode) to protect the system from a rectifier tube short
I have seen the diodes, but never used them. Great suggestion. The amp is up and running and all voltages check good. The 8k2 3 watt resistor took the fall. I have checked all the filter caps and they all read correctly. I am considering changing the 2 16uf's to 22uf/500. I have Dual 50/500 in place of the normal 33uf in the 18 watt. The rectifier short was caused because of a 1 ohm resistor to ground from each cathode. My inexperience in cathode biasing. At least this is my understanding. I did not know the cathode returned to ground through the resistor bypassed cap. I have a 5u4gb running well now. I will add the diodes as they are cheap and I have. I am no longer blowing fuses.
So what you are saying about the diodes is you connect the cathode to pin 4 and 6 and connect the wires to them? this keeps current from returning to the PT in case of a rectifier short.
I still have some changes to make to the PI resistors. Once I get everything just so, I am going to get all my readings so I can determine output wattage. It was an amp I built with parts I had left over from other builds and parts I had in boxes I bought at swap meets and antique stores and put into a 8 x 12 x 2 chassis. I did not expect such a nice sounding amp. I am going to tweak it, and build a cage top (something I am good at, metal work).
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BTW, I have a blank chassis, 17 x 10 x 2. I did some measuring and after I get all the kinks worked out, I am going to attempt to draw a schematic. Installed Visio today. If it turns out as well as I think it is, I am going to make another one. This one with a good parts and a touch more voltage from the PT. This will give me room for a loop, and reverb. Maybe KT-66's and I like that Brilliance idea from the Chiefton. I have built a really cool Bluesbreaker style pedal tremolo pedal which is really nice through an effects loop. I have a 2204 Marshall build and was reading a thread about Doug's loop. I was going to see how it would work in there. Looks like it is so simple it has to be great.
Sorry, I digress. I will report back after the PI changes and a couple of resistance dropping test in the B+. I would like to get back to a little over 400vdc at c1. Right now I am at 370, so I will look at a GZ 34 then a copper cap. It may end up being a SS rectifier, but I do prefer a little sag in this type of amp.
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So what you are saying about the diodes is you connect the cathode to pin 4 and 6 and connect the wires to them? this keeps current from returning to the PT in case of a rectifier short.
The SS diodes are just like having another rectifier in series with the tube rectifier. SS diodes only drop 0.6V each, so you don't notice that drop against the tube rectifier's (much bigger) drop. The tube rectifier still functions to drop voltage in the usual way (so you still get the desired B+ and sag etc in a PP amp); its just that the task of rectifying has already been done by the SS diodes - so if your tube happens to short, there won't be any high VAC on the filter caps, thereby avoiding that mode of failure.
Use 1N4007s. And yes, put one on each side of the high tension (HT) winding, in series with pins 4 and 6 (with the cathode/banded end of the SS diode pointing to the socket pin(s))
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IF you use ExpressSCH, you can easily edit this schematic into an 18w TMB preamp into a Cheiftain poweramp.
Since you are wanting to learn how to draw schematics, I won't do it for you.
With respect, Tubenit
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IF you use ExpressSCH, you can easily edit this schematic into an 18w TMB preamp into a Cheiftain poweramp.
Since you are wanting to learn how to draw schematics, I won't do it for you.
With respect, Tubenit
Thanks for the drawing!
I have Express, but the library is limited currently. I asked Steve and he said he used Visio and I saw components on his page I grabbed. I have not had a chance to check it out yet.
You did make a drawing, but it looks different in a few places. While grid resistors are normally 5k6 on EL-34, the Chiefton uses 10K. On pin 4 there is a series of resistors. 1k tied to 2 other 1k's going to individual pin 4's.
I really have no problem drawing as I am a Graphic Designer by trade and have been doing it since 1984, when the first MAC arrived. Before that I used drafting tools and freehand drawing.
My problem is deciding which program I am going to use. While Express PCB is quick and easy, I need to steal someone's component library. I have seen your layouts and they work well. I am very proficient in Adobe Illustrator, but Illustrator doesn't "store" a library. The problem I see with Express is that items are not scalable, so if you have a complex design, you must use additional pages as page sizes are limited. In Illustrator I can actually make a layout Illustration which looks like the inside of a chassis. Like you took a photo of it. But there again, I don't know if this is necessary. Also, I am very familiar with Autocad. When you export from Express it becomes an image which is not editable, so if you do not have the original .sch file to import you cannot edit it unless you use a raster program like Photoshop. You can however print it using Adobe Acrobat Driver and distill it to a pdf which then can be opened by Illustrator and edited and scaled. You have to clean up some random masks, but then you can join items together in groups and layers and scale them all you wish.
There are benefits to Express like exporting a build list and sending the file to have a PCB made. So I am in the decision process. I have your version open right now in Express and can edit it if I wish.
If you would kindly point me to a link where I can rip off a nice library of components, that would be cool. The program is very simple to use but being able to scale a group of items would be nice.
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point me to a link where I can rip off a nice library of components,
1) Anytime I want to draw a "new" schematic, I just grab an old one out of the
SCH library and begin altering it.
2) You can click on to any component and copy & repaste it ..... and then change
the component value. In other words, I will copy and repaste a capacitor &
then change the value
3) You can build your own component library VERY easily by simply clicking on to
a large section and "save as a group". For example: I have numerous
preamps, numerous tone stacks, numerous effects loops, numerous power
amps , numerous phase invertors, numerous reverb topologies, numerous
overdrives, etc......
To further illustrate: I have a Vox, Marshall, Fender, James, Dumblish,
5E3 and psuedo 5E3 tone stack all saved as a group/component.
I might grab an (input with paralleled triode), (then a triode with cathode follower), (then a HoSo56 tone stack), (then an LTPI), (then a PPIMV), (into a
6V6 power amp that is cathode biased), (using a PT & B+ rail).
Each of those is a grouped component that I've saved. So I simply insert those and connect the dots and change component values.
I do think you have very valid critiques on the limits of SCH especially when layouts are involved. I think Visio is much better but I don't have that program.
I like the simple editable nature of SCH. It's easy and quick.
With respect, Tubenit
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I like the simple editable nature of SCH. It's easy and quick
Me too
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I really don't have a problem using a combination of a few. Since I know Adobe Illustrator so well, I will certainly use it and have. There is no reason to stick with one program except to be compatible with others. I will simply look into Express, Visio and Illustrator and see how to use them together seamlessly. I want to be able to provide editable schematics for others to use. This is one of those areas where I feel I can give back a little of so much that has been given to me. I have been real busy with my real job that I haven't had the opportunity to explore. I soon will.
There is much to be said for simplicity and basic drawing functions. If your software fills the need, it is the correct one. It is all according to how you define simple. To me Illustrator is simple and I have not looked at Visio yet, but I'll bet it is simple as well to me. We will see. I will use whatever makes me compatible with the majority of the others. It does no one any good to create a drawing that cannot be used and adapted by others.
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I use Visio because I've been using it since it was a simple flowchart/organization chart program. I've owned every version since V1.
There's only a small group of Visio users here, mainly because the price is fairly high, unless you qualify for the Microsoft HUP. The schematics and layouts I make are very useful. The layouts are full scale, meaning anyone can print and just tape to a board to use as a drill guide. I convert to PDF format so anyone can use them. But, they can't be edited, unless someone has Visio and asks for the VSD file. Most Visio users here will share. Visio is almost as much fun as actually building an amp. And drawing schematics will help increase your knowledge of how these amps really work.
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I use Visio because I've been using it since it was a simple flowchart/organization chart program. I've owned every version since V1.
The layouts are full scale, meaning anyone can print and just tape to a board to use as a drill guide. I convert to PDF format so anyone can use them. But, they can't be edited.
Steve, PDF's can be edited. Pitstop is one program. There is a company called Quite which makes a whole line of PDF altering programs. Then a lot of PDF files can be opened in Adobe Illustrator and remain vector. You can export from here to cad if you want. That is why I am going to look into Visio. I have Professional 10. If I am able to open different platforms and maintain it as a vector it really will not matter where the original is created. Based on Adobe Acrobat Professional, there are many features and plug-ins for PDF editing. These are not free programs tho. That is the big advantage of a lot of the programs people use. Since I own a commercial printing company these are products that are just a part of doing business. We have to have many programs we do not make much use of. We use them to open customers files and export the file to something we can use in another program which is designed for graphic arts.
I am interested in Visio as I have heard lots about it and I assume it has a lot of nice features.
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Steve, PDF's can be edited.
I'm very aware of that. I use Acrobat Pro v9. But you can't do the kind of edits I was talking about, like adding another component, or re-routing a wire, or changing layers. Only Visio can do that.
BTW, I have a Visio format file of Rich's TMB layout. I didn't do it and it doesn't have any of my purdy components, but it's functional and might be a good way for you to get your feet wet.
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Steve, PDF's can be edited.
I'm very aware of that. I use Acrobat Pro v9. But you can't do the kind of edits I was talking about, like adding another component, or re-routing a wire, or changing layers. Only Visio can do that.
BTW, I have a Visio format file of Rich's TMB layout. I didn't do it and it doesn't have any of my purdy components, but it's functional and might be a good way for you to get your feet wet.
I would like to have it. You blocked personal messages from me. I wanted to send you my ftp info.
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I like to keep this stuff on the open board. Never know when someone else may benefit from our messages or have something important to contribute.
I'll attach the file here, but it will have a .pdf extension. Don't try to open it with a pdf reader. Just save to your computer, change the file extension to .vsd and open with Visio. I don't like a lot of things about this particular Visio file, but it will give you a "tip of the iceberg" working example of what Visio can do.
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I like to keep this stuff on the open board. Never know when someone else may benefit from our messages or have something important to contribute.
I'll attach the file here, but it will have a .pdf extension. Don't try to open it with a pdf reader. Just save to your computer, change the file extension to .vsd and open with Visio. I don't like a lot of things about this particular Visio file, but it will give you a "tip of the iceberg" working example of what Visio can do.
Thanks! I am a little greedy when it comes to data people have that I am interested in. I wanted to get you to dump your files on my ftp, that is why I wanted to send you the message.
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I like to keep this stuff on the open board. Never know when someone else may benefit from our messages or have something important to contribute.
I'll attach the file here, but it will have a .pdf extension. Don't try to open it with a pdf reader. Just save to your computer, change the file extension to .vsd and open with Visio. I don't like a lot of things about this particular Visio file, but it will give you a "tip of the iceberg" working example of what Visio can do.
I agree, but there are times where if a comment is posted public it can hurt feelings. It is difficult to convey voice in writing. The communication of programs is valid. But if I said publicly that I applaud you effort and work on programming Visio, but it is archaic and not very functional, that could easily hurt feelings. It seems as tho many get by with different formats and programs and they work well for their usage. So if the forum is designed to be public, I will post my findings publicly and leave it open for discussion. We will see the results.
Thanks for the file! I will use it to explore Visio.
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Installed the changes. I have a problem of very low volume. I changed the caps with new Mallorys (wanted to anyway), checked all resistors. Values all in check. I have 320 B+ and 317 on both plates of the EL-34's. I have 290vdc on the grids. The only thing left that I have not changed is the last filter cap and it is the 16uf cap. I have good plate voltage on all preamp tubes and the PI I have 217 and 215vdc. I can hear power, but it seems like the input source is low. I have replaced the bypass caps and resistors on v1. I have 18 vdc on the cathode. It seems as if the preamp section is not getting to the power amp section with enough amplification. Next I am going to use a boost pedal to hit the input harder and see if i get some volume. Who knows, I could have another OT that is toast, but it seems to have output on all 16-8 and 4 ohms. Maybe it is just a bad preamp tube.
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I have 290vdc on the grids.
Screen grid?
I have replaced the bypass caps and resistors on v1. I have 18 vdc on the cathode.
Which cathode, what tube? If it's V1 that has 18vdc, than that's what's wrong. It should only be a volt or 2, depending on how it's bias is set up.
Brad
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Sorry Brad, my post was rambling. The 18vdc is on the cathode of the power tubes. When I first built the amp, I used parts left over from other builds. Sluckey told me to change the resistor values of the PI to Chiefton values. While doing this I changed the caps in the amp with Mallorys as I had a hodgepodge of caps in the amp. All were the correct values, just different makers. I wrote the last post after being tired. I have shielded cable going from the inputs (there are only 2 inputs). One for the Normal Channel and another for the TMB channel. They are both Switchcraft 12A wired with a 1 meg through all and a 68k wired from the tip to shielded cable with the shield grounded at the buss ground and wire connected at V1 of both control grids. Grounded one end only. The bypass I was speaking of was V1B, I had a high value there and changed to 2.7K/.68uf.
When I changed the values of the PI to the Chiefton values the amp cleaned up a lot, but I also lost volume. Another thing that concerns me is the low B+ at the rectifier. With the power tubes out I have over 400vdc according to what rectifier I use. I did not expect 2, EL-34's to cause that much voltage drop.
I have a choke, Hammond 194c. It was between C1 and C2 which is a Dual cap. This is the first choke I have seen with a red wire and a back wire. Don't know why. I disconnected it and replaced it with a 270ohm/5 watt resistor to see if it may have gotten burned. Not the problem, but I have never seen a choke with 2 different color wires. Makes me wonder if it can only be connected one way.
I have individual resistors and caps on the cathodes. When I made the mistake of grounding the cathodes there is no telling what else got toasted.
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I have shielded cable going from the inputs (there are only 2 inputs). One for the Normal Channel and another for the TMB channel. They are both Switchcraft 12A wired with a 1 meg through all and a 68k wired from the tip to shielded cable with the shield grounded at the buss ground and wire connected at V1 of both control grids. Grounded one end only.
I'm not sure what your saying on how the input jacks are wired up, but each input grid of each preamp tube needs it's own 1M grid return R. So if you have 2 input channel jacks feeding 2 different input preamp control grids they each need their own 1M grid return R and the 68K R should be after the 1M to ground and not before it.
When I changed the values of the PI to the Chieftain values the amp cleaned up a lot, but I also lost volume.
That doesn't sound right. That could be what's wrong. EL34's take more voltage to drive them then EL84's, so I would think the Chieftain PI values would make for a hotter PI, which would _not_ cause a volume drop. Since the volume dropped after you changed the PI values, seems like that's the problem area. Check for miswiring, bad solder joint, wrong R values, the usual things.
I did not expect 2, EL-34's to cause that much voltage drop.
Might be running the EL34's too hot, which will cause the B+ to drop.
I have a choke, Hammond 194c. This is the first choke I have seen with a red wire and a back wire. Don't know why. I have never seen a choke with 2 different color wires. Makes me wonder if it can only be connected one way.
One color lead for the start of the wind and the other for the finish. It still can be hooked up either way, as most are, 50/50 shot, but hooking up the choke one way as opposed to the other will cause the chokes wire coil to act as a shield and will/should be quieter.
I'm just guessing, but I would think red goes to the B+ coming in to the choke and the black would be the output from the choke feeding the rest of the B+ going down stream.
Brad :think1:
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I have shielded cable going from the inputs (there are only 2 inputs). One for the Normal Channel and another for the TMB channel. They are both Switchcraft 12A wired with a 1 meg through all and a 68k wired from the tip to shielded cable with the shield grounded at the buss ground and wire connected at V1 of both control grids. Grounded one end only.
I have 1 input for the normal channel connected to V1A and 1 for the TMB channed connected to V1B. The input jacks are wired just like the single photo in Dougs libraty. A 1 meg resistor threaded through all solder points. Then I have a 68K resistor connected to the inner wire of shielded, the resistor is connected to the tip solder point of the jack, the shielding is soldered to the buss ground wire. At the tube the shielding is stripped, shrinkwrapped with only the cneter wire connected to the control grid. I did this as I wanted to use a regualr size pot for the Master. I don't care to have a low input for the normal channel.
When I changed the values of the PI to the Chieftain values the amp cleaned up a lot, but I also lost volume.
That doesn't sound right. That could be what's wrong. EL34's take more voltage to drive them then EL84's, so I would think the Chieftain PI values would make for a hotter PI, which would _not_ cause a volume drop. Since the volume dropped after you changed the PI values, seems like that's the problem area. Check for miswiring, bad solder joint, wrong R values, the usual things.
I rechecked. Removed all the resistors and put the meter on them. I have 1meg, left and right. I have 1.2K in the center, Brown Red Red and 47k on the top.
I did not expect 2, EL-34's to cause that much voltage drop.
Might be running the EL34's too hot, which will cause the B+ to drop.
It is cathode biased. I have 317 on the plates and 290 on the grids with a SS rectifier. My PT reads 650Vac Red to Red. I wanted a low power cathoed bias. Mullard Tube datasheet gives individual 270ohm, 350v in push pull. I am a little shy of that. If I bypass the choke I get very close.
I have a choke, Hammond 194c. This is the first choke I have seen with a red wire and a back wire. Don't know why. I have never seen a choke with 2 different color wires. Makes me wonder if it can only be connected one way.
One color lead for the start of the wind and the other for the finish. It still can be hooked up either way, as most are, 50/50 shot, but hooking up the choke one way as opposed to the other will cause the chokes wire coil to act as a shield and will/should be quieter.
I'm just guessing, but I would think red goes to the B+ coming in to the choke and the black would be the output from the choke feeding the rest of the B+ going down stream.
That is how I have it as I thought red was a for a reason.
Brad :think1:
I will continue retracing as I am sure I have done something stupid. I am using this project as a learning project. Eventually I want to be able to understand what each part reacts to current as well as the tonal changes of each. I played a new Fargen amp with parallel el-34's running very low wattage. Still had the feel of a big Marshall amp baking El-34's. It has gotten me interested in different usages of this tube other than lining up 4 of them ant ripping the paint f the walls. They have a unique and beautiful clean tone which is rarely taken advantage of. Since I play mainly Chicken Pickin you would think I would just get a blackface twin, but I have a very modified JTM-45 with EL-34's that really sounds good and has that Bakersfield tone nailed.
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I still think something in the PI is not right.
If when you changed the PI values and nothing else while you were doing that and then you had a volume drop, that's a red flag too me.
The voltages your geting for pre/post choke say it's droping 27vdc, which seems high for a choke in that position between the plate and screen supply nodes. This seems off too me. If you look at almost any Fender amp schemo that has a choke, their only droping a few volts or so across the choke.
When you write grid, which grid are you refering to? Power tubes, (tetrode, true pentode/beam pentode) have more than one grid. In a tetrode/pentode, G1= control grid, G2= screen grid, and in a true pentode, G3= suspressor grid and in a beam pentode G3 = beam forming plate.
If you mean screen grid, you can just write screen and then it's clear which grid your talking about.
I think it's gonna be a great sounding amp Ed when your done.
Brad :icon_biggrin:
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Found the problem. The 1.2k had drifted very high. Replaced it with a dale 1% and the volume correct. The normal channel sounds great at full. I have some tinkering to do in the TMB channel. I have a squeal coming from the master volume after about 3/4 up. Does it without any input. I have a 500kL right now. Had a 1 meg, but the 500 sounds better. They both squealed. It is sort of interactive with the treble. I changed the lead dress, no help. I also have too much voltage in the preamp. Could have something to do with the squeal.
Not from tubes. I think I am getting some DC on the master, but I have a .02uf cap before it.
I am tired right now, so time for a break. I will take all of the voltages later and post them. The voltages between pin 3 and 4 on the El-34's have gotten very close. I have moved the choke down between c2 and c3. I have a 270ohm/3 watt resistor between C1 and C2. I got an increase in the overall B+, but the 8.2k resistor connected to c3 which is now 22uf/500v is giving me about 317 vdc on the plate resistors. I have not gotten any further. Like I said, I will get all voltages and post them.
The amp sounds great. Lacks bottom on the TMB channel. I will get it worked out. It overdrives easily and the distortion is very pleasing, but lacks sustain and I cannot get it to feedback so playing Stranglehold is out of the question. I have a good handle on the components are interacting so it should be no problem to get it like I want it. I think there is a better way to implement a master volume.
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I have some tinkering to do in the TMB channel. I have a squeal coming from the master volume after about 3/4 up. Does it without any input. I have a 500kL right now. Had a 1 meg, but the 500 sounds better. They both squealed. It is sort of interactive with the treble. I changed the lead dress, no help. I also have too much voltage in the preamp. Could have something to do with the squeal.
Not from tubes. I think I am getting some DC on the master, but I have a .02uf cap before it.
The lead dress in those pictures you posted looks a bit suspect to me - wires going all over the place. You say you changed it - can you post a new pic?
You say its not a tube, but did you swap that pre-tube anyway?
The only other thing I can think of that could (sometimes) cause 'squeal' is a disc ceramic cap.
The only way to check DC on a cap is to lift the end of the cap and measure the DC. The pot would be scratchy if there was DC.
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I have some tinkering to do in the TMB channel. I have a squeal coming from the master volume after about 3/4 up. Does it without any input. I have a 500kL right now. Had a 1 meg, but the 500 sounds better. They both squealed. It is sort of interactive with the treble. I changed the lead dress, no help. I also have too much voltage in the preamp. Could have something to do with the squeal.
Not from tubes. I think I am getting some DC on the master, but I have a .02uf cap before it.
The lead dress in those pictures you posted looks a bit suspect to me - wires going all over the place. You say you changed it - can you post a new pic?
You say its not a tube, but did you swap that pre-tube anyway?
The only other thing I can think of that could (sometimes) cause 'squeal' is a disc ceramic cap.
The only way to check DC on a cap is to lift the end of the cap and measure the DC. The pot would be scratchy if there was DC.
First off let me say the squeal is coming from something dumb I have done. I get in a hurry to often.
I changed the preamp tubes with many different ones. They are all 12ax7. I have a lot of tubes. Yes, I did rewire, but I do have a small area to work in. The normal channel does not squeal at all. I have no ceramic caps. Pots are not scratchy. I cannot find the squeal by chopsticking it. The volume on the TMB channel is a lot louder than the normal channel. It is really loud and distorts easily. It is really not a very loud squeal and only happens when you get the volume up all the way and the master at about 3/4th. It is faint, but cuts off all the output sound. Like if it were a bad pot. The new wires go direct with none crossing another from the board to the pots. Of course some cross from pot to pot. Squeals are usually tubes, OT phase, lead dress or too much gain or resistors too far from the tubes, from what I have experienced. I've got some 5751's and some 12ay7 I can try, but it should run the 12ax7.
I will be doing some tweaking to the tone stack so I will be redoing some of the lead dress. When I get it all worked out, I am going to disassemble it and put it into a 17 x 8 x 3 chassis. That will give me the opportunity to to do proper lead dress, add a loop and reverb. It is worth the effort as it really sounds nice.
I mentioned the Master before. It seems like you get an awful lot of distortion from this setup. Maybe it is supposed to be this way but I don't use a lot of distortion so I keep it low.
I'll do some more checking
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It is really not a very loud squeal and only happens when you get the volume up all the way and the master at about 3/4th. It is faint, but cuts off all the output sound.
That sounds like a parasitic oscillation.
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I checked a few things. Touching the caps and wires leading to the tonestack causes noise. I have used fender cloth wire to rewire the tonestack. All is separate but poking around makes noise. Using a chopstick it is very minimal.
I have a buss ground tinned made from 12ga solid copper. It is bolted to the chassis. One ot 2 grounds, the other is a PT bolt.
I did get voltage readings
v1-1 205
3-1.86
6-156
8-.95
v2-1 226
2-38
3-59
6-230
7-40
8-59
v3-1 158
2-0
3-1.75
6-277
7-154
8-160
Power Tubes
v4
1,8-18
3-347
4-312
5-.03
v5
1,8-18
3-344
4-312
5-.02
I don't know if this will help. It seems like I may need to remake the ground buss. The OT is huge and right above the area which makes the most noise except the normal channel is perfect and sounds great. Great clean tone.
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It is really not a very loud squeal and only happens when you get the volume up all the way and the master at about 3/4th. It is faint, but cuts off all the output sound.
That sounds like a parasitic oscillation.
Yep, I tend to agree. I have had this before. I do have a lot of components in a very small chassis. I will mount the resistors to the tubes. Add some more shielded wire. Make a new ground bus. Increase the grid stoppers to 5.6k on the El-34's. What blows my mind is it does not show up on the normal channel at all and it is wired exactly the came. I did use a xicon poly cap on one of the bypass caps on v1 as I did not have a .68uf in an electrolytic. I have done this many times and never caused a problem. Hell, I don't know but at least i've got it playing and it does sound great. The problem has no effect really because I don't play that loud anyway. I didn't even hear it until i unplugged the guitar and turned up the volume knobs to see how much noise the amp made.
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What blows my mind is it does not show up on the normal channel at all and it is wired exactly the came.
The channels are nothing alike. The TMB has one more gain stage than the Normal channel. It is more prone to squealing than the Normal channel.
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What blows my mind is it does not show up on the normal channel at all and it is wired exactly the came.
The channels are nothing alike. The TMB has one more gain stage than the Normal channel. It is more prone to squealing than the Normal channel.
What I meant is they are wired using the same type of wire. It is very sensitive in there. The additional gain stage is where the components are the most sensitive. There is really no trick to this, I just have to break out some shielded cable and rework the ground buss. Obviously the 18 watt layout needs a little more shielding when using EL-34's.
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Changed position of the ground bus and ran shielded cables to the volume and master. Shielded cables from input jacks with resistors connected to v1 tube. The fender cloth wire just would not cut it. Everything is fine, just want to get more bottom end now. The tmb channel does not have the tonal changes I would like. I would like to get it closer to a blackface bass response.