First amp build

[sluckey]

Grid-41VDC

That's way too much bias voltage. Should be about -15v for EL84s.

[Mongrel714]

Grid-41VDC

That's way too much bias voltage. Should be about -15v for EL84s.

How do I go about fixing that?, Ive noticed Ive left off some ground wires, Im fixing that, then I will re check.
Thanks for the comment !!

[Adrien]

Is that +41 or -41V? Looks like your bias diode is backwards. Fix that and double check before you put the tubes in again! The bias voltage should be negative relative to ground. 

[Mongrel714]

Is that +41 or -41V? Looks like your bias diode is backwards. Fix that and double check before you put the tubes in again! The bias voltage should be negative relative to ground.

Ah ok, thank you, will do!

[Mongrel714]

The bias resistors are backwards!

[Mongrel714]

Well didnt help much, heres what were running now,
B+ These measurements are off the can caps,
1-405VDC-405
2-369VDC-369
3-335VDC-335
4-331VDC-328
EL84, off the pins,
Plate-403VDC-405
Grid-41VDC-25
Screen-369VDC-370
I'm running 100k resistors on pin 2 The grid, what really bothers me is there is 404VDC going to the Stand by switch, rated for 250VAC, I'm kinda baffled here, do I add some more dropping resistors? Thanks for any help!

[sluckey]

Looks like your bias diode is backwards.

Let me repeat, this time a little louder... YOUR BIAS DIODE IS BACKWARDS!!!!!

[Mongrel714]

Looks like your bias diode is backwards.

Let me repeat, this time a little louder... YOUR BIAS DIODE IS BACKWARDS!!!!!

Sorry, I'm usually not this air headed, I did turn around the two resistors instead of the Diode, I mis read.

[Mongrel714]

Ok, now on pin 2 the volts go up to around 7 then back to zero and stay there, Ive got the meter set on 20vdc.

[sluckey]

Ok, now on pin 2 the volts go up to around 7 then back to zero and stay there, Ive got the meter set on 20vdc.

That's still not good. I suspect you may have damaged the two 10µF bias caps when the diode was backwards. Replace them.

Take both EL84s out of the amp and don't put them back in until you can measure approx -15V (that's negative 15 volts) on pin 2 of both EL84 sockets.

[Mongrel714]

Ok, did some research while I was at work today, I had the Bias voltage coming from the tube rectifier, which is wrong, un hooked that, soldered it to the HT lead out of the power transformer and boom, uh no, not boom, it worked,  I have -41 volts! Turning the Bias pot went up to -61volts, Is that high? It was supposed to have a 50k trim pot on the board, I have a 25k Trim pot, so I wired up a 50 k pot instead, have to find out if that is wired correctly or not, You can see it in the pics, the wiper and right term wired together then to the 68k resistor, the right terminal to the 10uf cap and ground, let me know what you think ! Thanks a ton everyone!

[sluckey]

I've told you twice how much voltage you should have.

[Mongrel714]

I've told you twice how much voltage you should have.

Very sorry I asked again.

[sluckey]

No need to apologize. I'm not trying to discourage you. I know you are learning and I'm trying to help. Just wish you would listen a little more closely.

You're well on your way to having the bias voltage fixed. You just need to lower the bias voltage to work with EL84s. You can do this by increasing the size of R105. I suggest start with 220K and go up/down in size until you have about -15V on pin 2 of the EL84 sockets.

As mentioned earlier, I highly recommend replacing those two 10µF bias caps because they have been severely stressed when you had that positive voltage on them. There's a good chance that the EL84s are damaged as well.

[Mongrel714]

Thank you Sluckey, I do appreciate that, with my Job which is 10 hr days and a lot to do and take care of in my home plus car trouble and health stress I am a little frazzeled right now, I would not have started this project if I wasn't positive I could complete it, but I have stretched my self a little thin at the moment, But no worries, nothing a good nights sleep and a couple weeks vacation wouldn't cure!
  But really thank you, I give you the respect for your years of knowledge and thank you for passing it along!
I will be ordering some new caps and now tubes, and changing that resistor to find the correct value (when the new caps arrive!)

[Mongrel714]

Hey guys, Another question, I have a new choke, Hammond 194G, 3H @250mA, 79.92 Ohms resistance, At the moment this amp project has a 1,5K 5Watt resistor along with a couple more 10k 3 watt resistors and a 220k 3 watt resistor, in this resistor network, can I remove the 5w resistor and replace it with the choke, and would that help the power supply, or is this a try it and see type problem? I planned to use this choke on this project anyway, so what is your opinion?

[sluckey]

Don't do it! That 3H/250mA choke needs to have nearly 250mA current flowing through it to be effective. There is only about 15mA flowing through that 1K/5W resistor. The resistor will be way more effective than that big ole choke.

Read this google search for more details.

[Mongrel714]

Don't do it! That 3H/250mA choke needs to have nearly 250mA current flowing through it to be effective. There is only about 15mA flowing through that 1K/5W resistor. The resistor will be way more effective than that big ole choke.

Read this google search for more details.

Ahh, thank you, Ill save it for a bigger amp build, I knew you would have the answer!

[Mongrel714]

Working on the amp and my rectifier tube got mangled. I thought I would try a SS rectifier but even with a power resistor and a couple 10k 3watt resistors voltages coming off the rectifier is 413VDC,
at the EL84 screen grid its is 379V still -15 at pin2, But I guess Im ordering a new rec tube to get the voltages back down to a manageable level, unless there is another fix out there?? let me know, and thank you!

[Mongrel714]

I have ran over and over the schematics for the amp I am trying to build, and I'm finally seeing how the schematics applies to the layout, and the more I check the work I've done on this thing, the more correct it seems, as far as how I have it all hooked up, If I can get the voltage right, barring any bad solder joints or failed parts, I believe when I load up the tubes I will have a positive out come, even with the voltage as it is, there are no parts burning or smoking when I'm testing, My current limiter bulb is not lit, I've just got to get my new Rectifier tube and my new caps in and hopefully we'll be making some noise with this thing!

[AlNewman]

Nobody really knows what you've built at this point.  Tubes won't burn, they'll just break down, and when they do, they could wipe out every other part in the circuit they're attached to.  I suggest you copy the schematic you used, and use a program like paint to indicate any changes you made to the design, and then make a voltage chart at idle for every node on the power supply and pin on the tubes.

It seems to me you're running pretty high voltage for EL84's.

[johnnyreece]

Just going to chime in to say it sounds like your current limiter is likely mis-wired.  Given the other issues you've had, I would think you would absolutely want that working, just in case. 

[Mongrel714]

Nobody really knows what you've built at this point.  Tubes won't burn, they'll just break down, and when they do, they could wipe out every other part in the circuit they're attached to.  I suggest you copy the schematic you used, and use a program like paint to indicate any changes you made to the design, and then make a voltage chart at idle for every node on the power supply and pin on the tubes.

It seems to me you're running pretty high voltage for EL84's.

All right, thank you for the reply, I will do that, The circuit Im using is the "Tube Town" JC 18, I listed earlier, but yes Ive changed out some resistors so I will do the layout and voltage as asked, do I measure with tubes in or out? as it is right now, I have my B+1 and B+2 in the ballpark for voltage, my Neg bias is at -15VDC also, But I will sit down tonight or sometime tomorrow and layout all this and post it, thank you again!

[Mongrel714]

Just going to chime in to say it sounds like your current limiter is likely mis-wired.  Given the other issues you've had, I would think you would absolutely want that working, just in case.

Yes I would say your right, I am working on that right now, hopefully will have that fixed soon.

[AlNewman]

Although I think you may have skipped this step, normally it's a good idea to follow some sort of start up procedure.  Here's a link to a good thread.

https://el34world.com/Forum/index.php?topic=2376.0

Once you've found out everything is running properly, then measure voltages with tubes in.  Hopefully you haven't damaged your power tubes already when your bias voltage was missing.

You installed the 1R resistor at the cathode of the power tubes?  That measurement is important.  Otherwise, you'll have to measure resistance across the transformer to find current of the power tubes.

Don't forget to measure AC voltage at the heaters.

[Mongrel714]

Although I think you may have skipped this step, normally it's a good idea to follow some sort of start up procedure.  Here's a link to a good thread.

https://el34world.com/Forum/index.php?topic=2376.0

Once you've found out everything is running properly, then measure voltages with tubes in.  Hopefully you haven't damaged your power tubes already when your bias voltage was missing.

You installed the 1R resistor at the cathode of the power tubes?  That measurement is important.  Otherwise, you'll have to measure resistance across the transformer to find current of the power tubes.

Don't forget to measure AC voltage at the heaters.

Actually I have followed that, just have to go over it again, I have a tube tester and all the tubes are in the 90+ range,  the tester was recently calibrated and resistors replaced, The 1R resistor is a bias test point on the schematics, In just about finished with the amended schematics and layout, will include the heater voltage on that

[Mongrel714]

Hey guys, here's where I'm at so far, still have not put tubes in to try, I wanted to see if the voltages were in the safe zone to try, (the "Uncle Doug" video I watched says they are in range, although the PI may be a bit low)
Rectifier-+352V
B+1-+270v
B+2-+261v
B+3-+120v
B+4-+121v
EL84
pin 7-+268V
pin 9-+257v
PI
pin 6-+122v
pin 1-+122v
Pre amp
pin 6-+122v
Filiments-3.6vac
Bias--15vdc
I have listed changes on the layout, still working on the schematic.

[AlNewman]

No tubes?
Schematic needed.

[Mongrel714]

heres schematics, its 5:30 am, will do voltage when I'm awake this afternoon.

[ac427v]

Screen resistors are usually 100 to 470 ohms not 470K ohms. Typo? If you are using these values to reduce the B+ voltage they will overheat and burn. I suspect your donor power transformer makes too much voltage for your power tubes. However it might be suitable for 6V6GT???
Use separate 1 ohm resistors on each tube to measure tube bias. These numbers should be mv (millivolts).
Measure bias voltage where R21 and R22 connect to each other. This number should be volts

[sluckey]

In your effort to make the power supply voltages match the original schematic with no tubes installed you have really messed up the dropping resistors. I suggest putting the original resistor values back in and also removing that 20K that's between the diodes and the first filter cap. Then put the tubes in and connect the power cord directly to the wall. Your lightbulb is no longer needed. Now your power supply will have a proper load, and your voltage readings will be realistic.

All those voltage readings with the amp plugged into a lightbulb limiter and no tubes plugged in are really meaningless.

[Mongrel714]

Ok, will do that tonight, I was following a another build with the same kind of components (Hammond transformers) so that's the reason for the odd values, yes that was a typo, the amp had EL84s in it when I removed it from the organ, my lack of knowledge here has been a real handicap.
So thank you for the help guys.

[Mongrel714]

Screen resistors are usually 100 to 470 ohms not 470K ohms. Typo? If you are using these values to reduce the B+ voltage they will overheat and burn. I suspect your donor power transformer makes too much voltage for your power tubes. However it might be suitable for 6V6GT???
Use separate 1 ohm resistors on each tube to measure tube bias. These numbers should be mv (millivolts).
Measure bias voltage where R21 and R22 connect to each other. This number should be volts

AC, help me to get this through my thick skull, Do I connect the 1K resistor(s) to the points where r21 and r22 come together, and run it to the EL84 sockets on pin1? or do I replace the 100k resistors with the 1K?
Oh, and the screens on the Tube Town schematic are using a 1k/2w resistor, should I go woith the range 100 to 470ohm or stick with the 1k/2w?

Ive included the original Schematics for the Hammond organ amp, the power tubes use 6BQ5 there.

[Mongrel714]

Screen resistors are usually 100 to 470 ohms not 470K ohms. Typo? If you are using these values to reduce the B+ voltage they will overheat and burn. I suspect your donor power transformer makes too much voltage for your power tubes. However it might be suitable for 6V6GT???
Use separate 1 ohm resistors on each tube to measure tube bias. These numbers should be mv (millivolts).
Measure bias voltage where R21 and R22 connect to each other. This number should be volts

AC, help me to get this through my thick skull, Do I connect the 1K resistor(s) to the points where r21 and r22 come together, and run it to the EL84 sockets on pin1? or do I replace the 100k resistors with the 1K?
Oh, and the screens on the Tube Town schematic are using a 1k/2w resistor, should I go with the range 100 to 470ohm or stick with the 1k/2w?

I've included the original Schematics for the Hammond organ amp, the power tubes use 6BQ5 there.

All right, Duh, On the EL84 socket, pin 1 is just acting as a terminal point to connect to the resistor going to pin 2, so do I remove the existing resistor, replace with 1k, and then check the Bias voltage in mA at the junction of R21 and R22?

[Mongrel714]

In your effort to make the power supply voltages match the original schematic with no tubes installed you have really messed up the dropping resistors. I suggest putting the original resistor values back in and also removing that 20K that's between the diodes and the first filter cap. Then put the tubes in and connect the power cord directly to the wall. Your lightbulb is no longer needed. Now your power supply will have a proper load, and your voltage readings will be realistic.

All those voltage readings with the amp plugged into a lightbulb limiter and no tubes plugged in are really meaningless.

I agree with you, I've messed this up, my problem is this amp originally ran a 5U4gb rec tube which gave up the ghost, no telling how old it was, so I probably need to order another rec tube because the voltage is higher using the SS rectifier, which is where all my voltage problems are coming from, if I remove the 20 k resister the voltage will jump back up, so I guess Ill get another 5U4gb before I try this again?

[AlNewman]

I think the drop you're expecting from the 5u4 is likely current based.  Since your amp is only drawing a quarter of the rectifier's capacity, you may only drop 10-15V, compared to a perhaps expected 40-50V.
I may be wrong though.
What made you believe your rectifier is blown?

[Mongrel714]

I think the drop you're expecting from the 5u4 is likely current based.  Since your amp is only drawing a quarter of the rectifier's capacity, you may only drop 10-15V, compared to a perhaps expected 40-50V.
I may be wrong though.
What made you believe your rectifier is blown?

The silver on top of the tube has "evaporated" for lack of a better word, it is gone, and the tube will not light up in the amp, or in my tube tester, which is a B&K 600 Dyna Quick, as mentioned was recently gone through, the man I bought it from was retiring, he replaced the resistors. I'm not familiar with the quality of the performance of this tester, my EL84s are showing 90 on a scale of 0 to 120, and pass a grid emission and short test.

[Mongrel714]

Please forgive my being overly cautious here, but Ive left the power caps the same for this test, will be changing them now, I did change the Screen resistors back to the schematic value of 1K/2W, the Grids back to 100k, but plugged straight into the wall here are the voltages at the moment:
PT:333 vac
Rectifier: 344vdc
Heater: 3.5 vac
EL84
Pin 2: -15vdc
pin 3:0
pin 7: +250vdc
pin 9: +233vdc
12ax7
pin 1: +14vdc
     2: +0
     3: +0
     4: +3.5vac
     5: +3.5vac
     6: +24vdc
     7: +0vdc
     8: +1
     9: +3.5vac
Phase inverter
Pin1: +34vdc
    2: +17vdc
    3: +23vdc
    4: 3.5vac
    5: 3.5vac
    6: +33vdc
    7: +33vdc
    8: +23vdc
    9: +3.5vac
from what I have read these numbers are quite a bit off,
All your help is appreciated!

[AlNewman]

In your effort to make the power supply voltages match the original schematic with no tubes installed you have really messed up the dropping resistors. I suggest putting the original resistor values back in and also removing that 20K that's between the diodes and the first filter cap. Then put the tubes in and connect the power cord directly to the wall. Your lightbulb is no longer needed. Now your power supply will have a proper load, and your voltage readings will be realistic.

[ac427v]

AlNewman and Sluckey said it well.
Fix that power supply and remeasure voltages to start troubleshooting with good data.

[sluckey]

PAY ATTENTION! YOU'VE BEEN TOLD WHAT TO DO! MORE THAN ONCE!

[Mongrel714]

PAY ATTENTION! YOU'VE BEEN TOLD WHAT TO DO! MORE THAN ONCE!

You know  I appreciate your knowledge of this subject, and that you share it so freely, but forgive me, I cant afford to replace components left and right so I am just trying to make sure I don't fry something, I was told there are no stupid questions, apparently that is not true, if my questions bother you please dont answer them.

[Mongrel714]

Guys I am sorry if I am redundant in my questions, I'm just trying to be sure I don't mess something up.

[Mongrel714]

All the power supply resistor values have been put back to schematic, JUST as a precaution I measured without tubes first,
P.T.  332vac
Rectifier: +449vdc
B+1: +450vdc
B+2: +425vdc
B+3: +357vdc
B+4: +348vdc
EL84
Pin2: -15vdc
    3: 0
    6: 0
    7: +442vdc
    9: +425vdc
12ax7
pin1: +361vdc
    2: +0
    3: +0
    4: 3.5vac
    5: 3.5vac
    6: +368vdc
    7: +0
    8:  0
    9:  3.5vac
Thank you

[sluckey]

I was told there are no stupid questions, apparently that is not true, if my questions bother you please dont answer them.

I mostly believe there are no stupid questions. But you have repeatedly ignored the good advice you've been given. I find that frustrating. If I had known this was where this thread was leading, I would have bailed a long time ago. Well, I'm gone now. I'll probably continue following this thread purely for my amusement. Be careful. Bye.

[Mongrel714]

With tubes in the screen and plate voltage still were +440vdc pins 1 and 6 on the 12AX7 was +357vdc.

[AlNewman]

https://www.thetubestore.com/preferred-series-7189-premium-el84

Datasheet
https://www.thetubestore.com/lib/thetubestore/Preferred-Series-7189-Data-Sheet.pdf

Note, due to the internal connections at pins 1, 8, and 6, you'll have to reroute your screen resistors, and any other jumped connections from these pins.

[ac427v]

B+ is too high. What does it measure when you install a rectifier tube?
It appears that the AO39 power amp used a 5U4GB and two 6BQ5. It worked for Hammond. It should work for you. Hammond used 10 watt dropping resistors and two 30uf capacitors in the B+ feed.
Sluckey has been down this road. See his conversion!!!
https://www.sluckeyamps.com/hammond/hammond_ao39.pdf
The cap can next to the power transformer looks very old. Does it test good?
more conversion problems solved at:
https://sluckeyamps.com/index.htm

[Helmholtz]

The back-bias resistors in the Hammond power supply lower B+ by 28V.

[astronomicum]

The layout indicates 9V caps in the Bias supply. Should be a minimum of 63V based on a calculated Bias range of -11VDC to -49VDC with a 25K Bias pot. Typo or problem?

Is the B+ high because there are no power tubes in or they are not conducting?