Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Boone on September 17, 2013, 06:35:47 am
-
Hello everybody , I am new to the forum and have minimal experience with tube amps. I have one amp tech in my area. He seems to be not up to par so I am hoping you folks can guide me through my amp concerns : I have a Tweed Princeton clone with a Silvertone 1481 OT and a std Fender Princeton PT. The schematic for 5F2-A calls for a 10k and 22K voltage drop resistors. Tech must have misread value and placed a 100K and 22K respectively . 1st question : will the 100K result in tubes going bad prematurely due to incorrect voltages? 2nd question : how do I take voltage readings on the 6V6GT and 12ax7? I have built a mission 5E3 but am clueless on the workings of tubes. In light of that, please refer to pin#'s and not ( grid, plates etc...). I have a boatload of NOS tubes and just want to make sure the amp is not putting incorrect voltages on both tubes. Thanks for your time and help, it is greatly appreciated.
-
1st question : will the 100K result in tubes going bad prematurely due to incorrect voltages?
No. But the amp probably wont be all it can be with that 100K.
2nd question : how do I take voltage readings on the 6V6GT and 12ax7?
Set your meter to read DC volts. Connect the black lead to chassis ground. Now connect the red probe to each tube pin. Just hold the probe on the pin, taking care not to slip and short out adjacent pins. The pins you need a reading for on the 12AX7 are 1, 2, 3, 6, 7, 8. The pins you need a reading for on the 6V6 are 3, 4, 5, 8.
Be careful!
-
DC volts: is that the setting with ~ sign ? Also- I will post readings soon to get advice. Thanks for the help!
-
Note: rec tube is 5Y3 and cathode resistor is 470. Readings: 6V6- #3(408V) #4(183.2V) #5(.973V...this reading varied .875-.975V)#8(12.56V). 12ax7: #1(108.3V)#2(8.5mV)#3(.722V)#6(106.8V)#7(17.5mV)#8(.6mV).....any thoughts?
-
DC volts: is that the setting with ~ sign ?
No it's not. ~ means AC. What brand and model meter do you have? Post a pic if you can.
any thoughts?
Yes. Replace that 100K with a 10K 1 watt (or higher wattage). That will get the 6V6 pin 4 reading up to where it should be for a 5F2A amp.
-
Any thoughts on the readings re 6V6/12ax7? 408V on pin3?!!!
-
408V on pin3?!!!
While that may be a little high, it will not cause any problems. Change the resistor and that will get the 6V6 conducting harder which will probably bring that 408 number down.
Another easy way to lower that voltage is to use a NOS 5Y3.
-
I have a JAN Phillips 5y3 in there now. Have tried my JAN Hytron and GE 5y3 as well. Maybe a diff PT is in order here?
-
Replace that 100k resistor with a 10k as sluckey suggested and retake all your voltage readings and post them.
-
I will replace with 10K and keep you posted.......thanks
-
I swapped in 10K : 6V6gt is now red plating. Readings: 6v6- #3(364.5V) #4(315.5V)#5(3.7V)#8(23.85V). 12ax7- #1(167.5V)#2(28.8mv)#3(1.428V)#6(169.7v)#7(1.0mv)#8(1.398v). Note: after I got amp back with 100k in there (where 10K is now) amp broke up a lot sooner and did not red plate . Any thoughts with new readings ?
-
I may have to also point out: this amp only has 3 filter caps from left to right:20uF,10uf and 8 uf. On board between 20 and 10uf is the new 100K. Between the 10uf and 8 uf is the 22K. Thanks for all of your help folks!
-
Sorry re above reply: between 20uf and 10uf is new (10K)......
-
Pin 5 of the 6V6 should have 0 volts. what is the actual ohms of the cathode resistor connected to pin 3 of the 6V6? The tube is biased way hot. You may need a 680+ ohm resistor?
-
I have a 10watt 470 in there with 10uf 250V in parallel.
-
Try a 680 ohm 5 or 10 watt resistor if you have one and see what happens.
-
With regard to all readings or just #5 on 6v6?
-
Can you adjust your meter to not read mV in the DC setting? The new voltage readings look to be normal except pin 5 on the 6V6.
-
Excuse the wet behind the ears.... VOM directions say to set meter to auto- I did that. What would rc look like : one setting has ~ (AC) I see, and - sign with mv at bottom left hand corner.
-
What make and model meter are you using? Do you have a 680 ohm 5 or 10 watt resistor to replace that 470 ohm cathode resistor thats in there now?
-
Meter is a piece of poop cheapo type Radio shack. I know......I just ordered a 10 watt 680 and 700 ohm clarostat power resistors. Here's my concern, the amp with the 100K (1st power resistor) sounded pretty good. I read somewhere that some other deal in the 6v6 should be balanced or not to exceed the plate voltage). So I was concerned that the screwy 100k was putting undue stress on tubes. I agree with the previous post that bias is up there now. I guess it's just impossible to get this thing to work at correct voltages,amp and bias with the 470 in there. Is it a common practice to increase to 680 and still have all pins and bias fall into correct specs? Bear with me here, I am obviously an amature at this . I also have a boat load of NOS tubes that I inherited and would like to use them for audio not a light bulb. Thanks for the thoughts everybody!!!
-
I also have a boat load of NOS tubes that I inherited and would like to use them for audio not a light bulb.
If you have a bunch of different 6V6's then start popping them in 1 by 1 and you might find 1 that doesn't red plate.
All tubes even from the same manufacturer will draw a different amount of current.
Brad :icon_biggrin:
-
How do I figure bias? I have a 1 ohm I can to one of the 6v6 pins...I don't which one to ck bias with.Amature here: step by step please- also what are parameters for hot/safe bias and cold/safe bias? Thank you
-
Hey Willabe, the tube the was not red plating before the resistor swap red plates after 10k soldered in......
-
How do I figure bias? ... what are parameters for hot/safe bias and cold/safe bias?
Well, it's a cathode-biased amp, so you shouldn't have to figure anything. The tube settles in on whatever idle current it decides as a result of the cathode resistor value.
For a single-ended amp like yours, "hot, safe bias" is redplating but just enough cooler to stop the redplating. Or 100% of the plate dissipation rating, which is 12w (or 14w if you choose the later number for the 6V6).
"Cool, safe bias" is no current, stone dead. But that wouldn't be a good amplifier, so anything above 0mA of idle current that doesn't sound nasty at low volume to you.
Most people idle at 100% plate dissipation, because in a single-ended amp anything less just gives you less output power.
How do I figure bias? I have a 1 ohm I can to one of the 6v6 pins...
Unsolder the cathode resistor from pin 8 of your 6V6. Solder one leg of the 1Ω resistor to pin 8; solder the other leg to the free leg of the cathode resistor (which used to go to pin 8). Now, if you measure d.c. volts across the 1Ω resistor, the number will directly convert to the # of d.c. milliamps of cathode current.
But power = voltage * current, and you need the voltage part of that. Place you meter's black lead on pin 8 of the 6V6, and place the red lead on pin 3. If you can clip these in place with the power off, so much the better. With power on, you will be measuring the voltage from plate to cathode, which the tube feels as its plate voltage.
Multiply that plate-to-cathode voltage by the number of milliamps you found across the 1Ω (in the form of 0.020, which equals the 20mA you would have if you measured 20mV across the 1Ω). This will be plate dissipation in watts.
-
Blueplates : I would rather not bother with this bias stuff either with cathode biased amp. I was just concerned about the 408 pin 3 , 187 pin 4 and .9V at pin 5 damaging tubes prematurely. I think the amp sounded fine as it was.....just wanted it back into specs so as to not damage tubes. Thanks for the lengthy bias direction, I will use that.
-
I was just concerned about the 408 pin 3 , 187 pin 4 and .9V at pin 5 damaging tubes prematurely. I think the amp sounded fine as it was.....just wanted it back into specs so as to not damage tubes.
Those voltages are perfectly safe for the tubes. If you liked the sound of the amp with those voltages, then put the 100K resistor back in the B+ rail. The tubes will be running cool and probably last forever.
-
One day I'll post a picture of a Westinghouse 6V6 I have.
I got the tube in a lot of tubes off ebay. It actually has a hole melted through the plate of the tube. Not a small one either, maybe 1/8" x 1/4". I put it on a tube tester and it came up fine. I've played it in amps and it sounds and works just fine.
I will admit I've not monitored its plate current over time to see if it was unstable, but it sure seemed to perform alright. That experience makes me think your tubes are fine. Plus, the way they were being run before (with the 100k in the power supply) just reduced the 6V6 current and power output.
-
One last question: I bet you folks have had it with this. If tubes are cool with the 100K I may put it back or try 50K-75K to see what it sounds like. I take it that is ok as well? Btw- I know everyone has the tone of tone amps . But this thing is effin LOUD with the 100k in there. Go figure.....cold tube= much vol. I have a 12" ceramic spk in cabinet. The tone/crunch is nice Sumlin type up until around 9 or so..... Go figure that out with cold tubes. A VERY BIG thank you everybody. Ps- anyone need some xtra cash? I need a (layout) drawn out for a 2x6V6 5y3. 12ax7 amp 1 vol 1 tone 2 input based on another amp. If anyone is interested we can correspond through email. Boone
-
Blueplates- please post pic of Westinghouse !! I'd like to see that. Thanks for all your time and effort folks.
-
... If tubes are cool with the 100K I may put it back or try 50K-75K to see what it sounds like. I take it that is ok as well? Btw- I know everyone has the tone of tone amps . But this thing is effin LOUD with the 100k in there. Go figure.....cold tube= much vol. I have a 12" ceramic spk in cabinet. ...
3-4w is plenty loud, especially if you have an efficient speaker. A Champ into a 4x12 cabinet is surprisingly loud.
But yes, you can experiment with higher-than-stock resistors in the power supply all you like.
-
Take a look at the Fender 5E3. http://www.webphix.com/schematic%20heaven/www.schematicheaven.com/fenderamps/deluxe_5e3_schem.pdf (http://www.webphix.com/schematic%20heaven/www.schematicheaven.com/fenderamps/deluxe_5e3_schem.pdf)
That will get you pretty close
-
Blueplates, are you referring to the 5000 and 22K? Is the 5000 a 50K? Thanks
-
Labb, does the layout you suggest call for a 5000(50k?) first then the 22K?
-
I think the voltage issue may be the PT: pin 2 and 8 on 5Y3 read 382V. PT is a TF22772. Any suggestions on a better brand type?
-
Pin2 and 8 on PT are red wires
-
Pin2 and 8 on PT are red wires
That's backwards.
Standard wire colors for PT B+ with a rectifier tube for high acv secondary are red/red and goes to rectifier tube pins 4 and 6. The red/yellow wire is the high acv secondary center tap (CT) and goes to ground.
Yellow wires are the 5acv for the rectifier tube heaters and go to pins 2 and 8. Take B+ dcv from pin 8.
Brad :icon_biggrin:
-
I think the voltage issue may be the PT: pin 2 and 8 on 5Y3 read 382V.
382??? How can that be. Your main concern was the 408V on pin 3 of the 6V6. But pin 8 of the 5Y3 is the ABSOLUTE HIGHEST VOLTAGE inside the amp.
I think you are obsessing over some very minor details.
-
Brad, the rec pins are marked as follows: I have a 5y3 tube that has 5 pins . Three on one side and two on the other. The #1 pin marked on socket is the ( middle) pin of the three on one side. Or the 1st pin just to the right or notch looking straight down on to the socket. Looking at it again- my bad: 2&8 have yellow wires, 4&6 have red, 8 has red wire going to first filter. Any thoughts on the 387V ?
-
That what I assumed too. I have no idea Sluckey.......what is typical v at pin 2 on rec socket? Aren't most Tweed Prince PT putting out 360v at 2/8?
-
Boone, you have the right power transformer for this amp and it is performing as it should. with the 10k resistor in the power supply all the voltages are normal. Pin 5 of the 6V6 you have 3.7 volts. Perhapes you ment to write 3.7mv? It is very common to have a 680 ohm or higher cathode resistor to cool down the bias on these style amps. When these amps were designed and built the wall voltages were 110vac at best. Now a days in some places they are over 125vac. I have built many of these style amps and had to increase the cathode bias resistor on all of them. Punky
-
Any thoughts on the 387V ?
Yes, it's fine, listen to Sluckey and punkykatt.
If it were me, I'd put the 10K B+ dropping R back in and add a 470R screen grid stopper. Then if I had a bunch of 6V6's I'd try and find 1 that didn't red plate. Then if I couldn't find 1 that didn't red plate I'd do what punkykatt said, increase the KR.
Brad :icon_biggrin:
-
Pinky, I hear you on the 680. With the 10K in there pin 5 on 6V6 is 1.47V. Any ideas?
-
680 and 700 are being shipped. Should the 680 take pin 5 down to zero? Thanks for your patience and help gentlemen and ladies.
-
Boone, you have the right power transformer for this amp and it is performing as it should. with the 10k resistor in the power supply all the voltages are normal.
When these amps were designed and built the wall voltages were 110vac at best. Now a days in some places they are over 125vac. I have built many of these style amps and had to increase the cathode bias resistor on all of them.
This is why I suggested to try and find a tube that would run a little cooler. They run a little hotter with the higher wall voltage.
If you happen to put in a tube that draws current on the high side plus with the higher wall acv, it can red plate.
Brad :icon_biggrin:
-
Hi Willaby, I hear you as well ....I was concerned I may wear out tubes prematurely even if they are not red plating. Kind of like running a 5 speed manual vehicle in 4th gear on the freeway...speed ok, temp ok but undue stress wear and tear on engine....... None of my NOS tubes red plate ..... This amp eats the current production Tung sol like popcorn. I use the Tung to practice with and the NOS for recording . You guys are whipping me into shape . I appreciate that. I feel I may have called in the Calvary for a very minor skirmish . Man, you guys are on this stuff like stink on a turd. A great VERY knowledgable group for sure. I will install the 680 and give you gents and ladies an update as soon as it arrives. I will figure bias as it sits now with the 470 and let you guys know soon. Thank you
-
Pinky, I hear you on the 680. With the 10K in there pin 5 on 6V6 is 1.47V. Any ideas?
It may be possible that the .022 coupling cap connected to pin 5 of the 6V6 is leaking DC voltage. That would be the cap also connected to pin 6 of the 12AX7. Unsolder the end that is connected to the 220k resistor on the board and lift it out so it is not connected to the circuit. with your meter set on DC connect the black (-) lead to the chassis and with the red probe see what DC voltage reading you get on the lifted end of the cap..
-
Punky, I will do that and get back to you. I have a friend who salvaged a toolbox full of old caps. I have a couple of red Sangamo in there right now. I will get back to you. Thanks for the efforts
-
Punky, started at 220 and quickly dropped and settled at 47.3V
-
Punky, started at 220 and quickly dropped and settled at 47.3V
Replace that cap with a NEW cap. Give that toolbox full of old caps back to your friend.
-
Will do Sluckey, I will take reading again after its replaced and post results. How do I test the cap near the 12ax7?
-
How many volts should read at the lifted lead with a good cap in there?
-
Punky, started at 220 and quickly dropped and settled at 47.3V
Replace that cap with a NEW cap. Give that toolbox full of old caps back to your friend.
:laugh:
Many of the old caps now +40/50 years old leak dc because of the way they were constructed and the materials they used to make them. And if it doesn't leak now it could or will soon.
You won't hear the difference with a new cap if you use a good one. Mallory 150's, orange drops will be fine.
Brad :icon_biggrin:
-
I have a couple of new Jupiter type mustards . They have black line at one end: should line go toward 12ax or input jacks?
-
They have black line at one end: should line go toward 12ax or input jacks?
Huh? There's no coupling cap between the input jacks and the 12AX7 grid.
Line, if it's really correctly marked, should go to the low impedance ac ground. So a coupling cap's outside foil when wired in between the 12_ _7 and the next grid would go to plate.
Brad :icon_biggrin:
-
Installed new cap , lifted top lead at 220r and could not get reading. VOM swinging wildly from 68-212 mV then back and forth over theses values.placed cap with black line toward input jacks.
-
How many volts should read at the lifted lead with a good cap in there?
Zero at idol with all controls turned to zero.
Brad :icon_biggrin:
-
Installed new cap , lifted top lead at 220r and could not get reading. VOM swinging wildly from 68-212 mV then back and forth over theses values.placed cap with black line toward input jacks.
Now with both legs of the cap properly in place, you should get 0vdc (o a very few millivolts) at pin 5 of the 6V6.
And not having d.c. leaking through will cure your redplating issue (most likely), so you won't need to tinker the cathode resistor value.
-
The tone/crunch is nice Sumlin type up until around 9 or so.....
Are you referring to Hubert? Most guys don't know about him.
Brad :icon_biggrin:
-
I was concerned I may wear out tubes prematurely even if they are not red plating. None of my NOS tubes red plate ..... This amp eats the current production Tung sol like popcorn.
And not having d.c. leaking through will cure your redplating issue (most likely), so you won't need to tinker the cathode resistor value.
Your not going to prematurely wear out the 6V6. Like HBP said most guys run them in a SE amp at 100 dissipation. That is what wears out tubes it's how hard you work them.
You can run them at, say, 200dcv on the plates at 100% dissipation too. It's not just the dc plate voltage, that's only part of the overall picture of how their run. Higher plate voltage/lower current, lower plate voltage/higher current. Both set ups can be biased to run at 100% or say 90%, 80% dissipation.
Brad :icon_biggrin:
-
I have a couple of new Jupiter type mustards . They have black line at one end: should line go toward 12ax or input jacks?
Here's a link that Tubnit started and is now in archives of favorite topics.
http://www.el34world.com/Forum/index.php?topic=11427.0 (http://www.el34world.com/Forum/index.php?topic=11427.0)
Brad :icon_biggrin:
-
Yes Brad Hubert Sumlin is a fine example of being underated. For anyone who wants to bask in his tone and more importantly his unreal delicate to low down masterfully placed runs go to : YouTube and pull up Smokestack Lightning.....the most perfectly placed riffs. Wolf, in my world , is the best male blues singer to walk the earth. His slide and harmonic playing is out in orbit as well. Wolf put together one tight groove machine! Hubert came to a Wolf recording session with a pick. Wolf said loose it or get out. It's all thumb in this band. Hubert played through a Danelectro 12-15 watter. Hubert is a big fan of LP's. Played Silvetones in the early days. I will change the shitty golden caps of yesteryear and get back to you guys. The Movie Cadillac Records is based on Wolf and Muddy's rise to fame at Chess. Check it out, there are some ass kicking remakes with Little Walter's harp going into a Tweed Deluxe . Low down dirty good stuff.
-
Installed new cap , lifted top lead at 220r and could not get reading. VOM swinging wildly from 68-212 mV then back and forth over theses values.placed cap with black line toward input jacks.
68-212mV is good. Just consider that to be zero volts leakage.
Replacing that cap fixed the problem with the pin 5 voltage reading. The tube should not redplate now. So, put that 10K resistor back in the B+ rail. This will cause the reading on pin 4 to increase to normal and your 408V reading on pin 3 will drop to a lower value. Leave the 470Ω resistor on pin 8.
The amp will now be all it can be. If you liked the starved sound with that 100K in the B+ rail you're gonna love the sound with the 10K in the B+ rail.
-
Swapped caps: 4.5 -6.7 mV at pin 5 . Reading is swinging up down and back btw these figures. Tube still red plating.
-
I will try to attempt a bias calculation with new caps and 10K in place. I think the Sol may have gone by by. Like Sluckey said it just may be a crappy tube. I will get this.... thanks for stay in' with me on this.Stink on a turd!
-
I knew Hubert. I can't say we were really friends but he knew would recognize me and sometimes remembered my name. :laugh:
I hung out in a couple of clubs/bars where he would play and hang out at sometimes when he was in Chgo.
I had a couple of friends that were smart enough and played well enough to play for Hubert. Curt Obeda (guitar) and Steve Arvey (bass).
One night I was working the door at a bar called "B.L.U.E.S." and Hubert was playing that night across the street at the "Kinston Mines".
Steve came over and asked if Hubert could play my guitar that night because Hubert left his on the band stand the night before. Hubert lost some guitars through the years doing that. :laugh:
Anyway Steve knew I always brought my guitar with me to work, at the time a re-issue 58 LP, so I could sit in at the end of the night.
I told him sure but keep an eye on it and make sure it doesn't grow legs and walk out the back door.
After B.L.U.E.S. closed at 2:00 AM we would all go over to the Mines and drink which was a 4:00 AM joint. Often I'd sit in over there too. Hubert sounded like Hubert as always, didn't really mater what guitar he was playing and that night for some reason he was smoking a big fat cigar.
He thanked me for helping him out that night, he was always very kind and always smiling/joking. One of the things the old blues guys would say to each other when they saw each other in a club was "Ill be glad when your dead and gone you rascal you." Then they'd laugh and laugh.
The next morning I got up opened up my guitar case and put a record on. I was getting my tuner out and started to notice a very, strong, bad, funky, smell. At 1st I couldn't figure out where it was coming from. :w2:
Then I picked up my guitar and smelled it. WOOW! It was from that cigar Hubert was smoking! :laugh:
Got out the lemon Pledge and drowned it 2/3 times and it was pretty good but it still lingered in the strings. :laugh:
Brad :icon_biggrin:
-
Priceless Brad. Holy Smokes! What a treasure to have hung out with one of the badass'! I am unclear on Wolf's death and the kidney issue... was Wolf around you at that time or was he ill?
-
Swapped caps: 4.5 -6.7 mV at pin 5 . Reading is swinging up down and back btw these figures. Tube still red plating.
According to the voltages you posted in a previous post with the 10k installed, the 6V6 is running at 123% max plate dissipation going by 14 watt mpd of the 6V6 or at 143%max plate dissipation of a 12 watt mpd 6V6. You better go with the larger cathode resistor IMO. Punky
-
No, Wolf passed in 76? I was 16/17 then. I started hangin out at some blues clubs in the early80's.
Hubert was as gentle as a lamb. He was really kinda shy. But a lot of young guitar players would search him out and he loved that. I never heard him say a bad word about anybody or to anybody. And that movie was way off on most of how they told the stories. Although Little Walter did
take the doors off of his caddy. :laugh:
I never met Wolf or Muddy but I did know a lot of their players. Sat in with a lot of them too. In the 80's blues was on life support and the guys who were left would sometimes play a night or just come around and hang out. They were just regular guys who loved to play blues. A lot of them were very kind to the younger guys and would let them sit in and you could ask them things but most of those guys really didn't know about amps and guitars except what they liked.
A lot of those guys drank pretty heavy at one time (in the Chgo. blues hay days, 50's/60's) so a lot of them really didn't remember
all that much about who was playin what back then, let alone what year model tweed or what tubes were in it. To be fair, even if they did say they remembered who was playin what, everyone's memory gets foggy after 20/30+ years. :d3:
Brad :laugh:
-
Get about 360 vdc (340 to 380) on the 6v6 anodes, select a cathode resistor (250 5 watt) that will give you a tube dissipation of a little over 12 watts (Leo ran the 5e3 hot) and let her bump. You will like it.
-
Get about 360 vdc (340 to 380) on the 6v6 anode, select a cathode resistor (250 5 watt) that will give you a tube dissipation of a little over 12 watts (Leo ran the 5e3 hot) and let her bump. You will like it.
That works well in a 5E3. But that 250Ω cathode resistor in this amp will probably roast the 6V6.
-
Yes Sluckey, Blueplates Punky Brad etc.... cant remember everybody. I am waiting on the 1 ohm to arrive to ck the bias. Should be here soon. Yes Stuckey I have the vol up there for the most part with this amp. Work the tube kinda hard.No Beast of Burden tones from this animal . Cleans are marginal and sound ok at low vol. This is my cruncher/blues amp. I am curious to hear this thing as it was designed. I probably will leave it set at VERY slight cold bias after all is said and done . After 1 ohm gets here I will take another round of readings, try to determine bias and see how the poor thing sounds. Man, I get the feeling that amp was on a constant uphill battle with the blown cap, wrong drop res and a bad tube.....I've been trying to get a 4 yr old to eat uncut string spaghetti with a spoon. Previous post explained bias ck very well and clear enough for a greenhorn like me to handle. However, brace yourselves.... you may need to coach me through bumps with the bias ck. Boone
-
Dang, I got confused and thought we were on a tweed deluxe. I have built the Princeton. It is a Champ with Tone control. I'm going to see if I can find my file and see what I ended up with for a cathode resistor.
-
You don't need a 1Ω resistor to do bias and static power calculations with a cathode biased amp. Especially on a single ended amp. Just measure the voltage on the cathode and divide by the value of the cathode resistor. The resulting current will be exactly what you would get by using the 1Ω resistor method.
-
I had modified the Princeton so much that it was of no help. Did look at the schematic for the Harvard, model 6G10, which is a lot like the Princeton. That schematic has voltages on it. Shows 350 vdc on the anode, 20 volt at the cathode and a 470 ohm cathode resistor. That would give you a plate dissipation of about 13.4 watts. Leo ran them hot. One thing that I do remember about the Princeton build was that as I raised the cathode resistor the anode voltage went up. I ended up using some zeners to drop B+. I'll get out of this conversation. Sorry if I have confused the issue.
-
You don't need a 1Ω resistor to do bias and static power calculations with a cathode biased amp. Especially on a single ended amp. Just measure the voltage on the cathode and divide by the value of the cathode resistor. The resulting current will be exactly what you would get by using the 1Ω resistor method.
Then take the plate voltage (pin3) and subtract the Cathode voltage(pin 8) Then multiply that voltage by the resulting currant amps as above will give you the watts the amp is taxing the tube. Divide that value by 12 or 14 (depending on the mpd rating of the 6V6 you are using) will give you the max plate dissipation of the bias. Watch your desimal points you may have to multiply by 100 to get the proper number. Check me guys, I`ve done it many times, but to write it out, not sure I worded it right.
-
#8 (22.05v) divided by resistor (470) = .04691489 #3 (370v) - #8(22.05v) = 347.95v. 347.95X .04691489 = 16.324036 Then multiply by 12 or 14 then X by 100 Punky?
-
#8 (22.05v) divided by resistor (470) = .04691489 #3 (370v) - #8(22.05v) = 347.95v. 347.95X .04691489 = 16.324036 Then multiply by 12 or 14 then X by 100 Punky?
He said divide (not multiply) by 12 or 14. This is just a way to state a percentage figure of your idle plate power in relation to the max plate power for a 6V6, which is 14 watts.
Your plate is idling at 16.32 watts. So, 16.32 / 14 = 1.17 x 100% = 117%. But this calculation ignores the current and power dissipated by the screen (pin 4), so the actual plate dissipation will be less than 16.32 watts. In fact, you're probably about on target for 100% dissipation. But since you are concerned with running the tube hot you'll probably want to replace the 470Ω cathode resistor with a larger value. If you do that you will need to measure the voltage on pin 3 and pin 8 again and recalculate.
If it were my amp I'd say 'well done' and just button it up as it sits right now.
-
Thank you everybody! I would say 'well done' to you folks. I will swap out the cathode res this evening,recalculate and post results.
-
Ok- 680 and 700 resistor not here yet . I decided to play the amp at current specs. The amp is squeaky clean. Breaks up too much later on the vol setting .Sounds more SF. I decided to compare V readings of GE vs RI Tung. GE is at 377 pin 8 and Sol is at 364 pin 8. I will measure #8 with a Westinghouse, Hytron RCA etc..... I will swap res's and keep you guys posted.
-
Anyone know to attach pics to this thread? After res swap- major noise issues with vol/tone maxed.
-
I think I figured the photo thing out. Will post pic later.
-
When you do a reply look in the bottom left corner and you'll see Additional Options, click on it, then click on browse. Find the photo/file and click on open. The name of the photo should appear in the Attach box. Then click post or save. (I also click on the Return to this topic when I post photos.)
Brad :icon_biggrin:
-
Hi Brad, I took pics to post. They don't do the job. Are you up for a lengthy description of whats going on with this amps layout? After the 10K swap I got all kinds of noise. This amp, prior to res swap, was dead quiet with all controls maxed on amp/guitar. I run P 90's through this amp. The "tech" that put it together had same noise issues.He eliminated components and moved things around. I got it back from him and the noise was there. I poked around with a wooden stick and come to find a cheap PC board speaker jack that was not making good contact with chassis or guitar cable. I replaced it and noise was gone. Now the gremlins are back after 10K was installed. I hope you guys can help with this. Boone
-
If you want a Princeton, I highly recommend you replace that little Silvertone OT with a tougher one.
-
... After the 10K swap I got all kinds of noise. This amp, prior to res swap, was dead quiet ... I poked around with a wooden stick and come to find a cheap PC board speaker jack that was not making good contact ... Now the gremlins are back after 10K was installed...
Odd noises in a new build are gonna be poor connections or poor solder joints, most likely. Your description of the noise and its past cause suggests as much.
-
Thanks Stuckey, Blueplateset etc.... I will check solder points again. If I find everything is tight. I think I am going to remove the pre amp section and build to 5f2a specs. For instance : the .0005 that goes btw the tone/vol pot -he has at far left bottom of board with wire traveling back and up to tone stack. I also have no lead coming of the dual 100K's that are placed in pyramid configuration at bottom right side of board etc.. ....
-
The lead that manipulates the noise (with movement) the most -but does not solve the problem : goes from the left 68K up to lug on input 1. I replaced wire with no result. Should I replace input 1 jack as well? The amp will make noise with no guitar in the signal.
-
Should I replace input 1 jack as well? The amp will make noise with no guitar in the signal.
Ground the input grid wire and see if the noise goes away. If it does than the switch on the input jack is not grounding the input preamp grid when no cord is plugged in.
Brad :icon_biggrin:
-
Do you mean the wire coming off the 68K that is manipulating noise levels? Remove that from input 1 lug and ground that wire? Or remove it from 68K then to ground?
-
The signal chain goes >input jack>68K>preamp tube grid, pin 2/7.
Ground the input signal with an alligator clip jumper wire. Probable easiest to clip it to the jacks tip.
On the input jack there's a switch that is normally closed. It goes to the input jacks tip. So when no jack is plugged in it grounds the tubes grid. Sometimes those jacks get bent or the contacts are dirty and the switch doesn't ground out the grid.
Brad :icon_biggrin:
-
I will do that and post back tomorrow with 680 installed. Thank you. Boone
-
If you want a Princeton, I highly recommend you replace that little Silvertone OT with a tougher one.
If you want a Princeton, I highly recommend you replace that little Silvertone OT with a tougher one.
If you want a Princeton, I highly recommend you replace that little Silvertone OT with a tougher one.
Probably a good idea Stuckey.....I have yet to hear a real Princeton live. However, this whimp of an OT distorts nice and can get close to Mick Taylor's dimed Ampeg when he played Carol on Ya Ya's Out album. I agree some more punch would be nice but this thing is perfect in the studio. I am still waiting for the 680 to arrive. I will keep you guys posted. Brad, the switch tab was dirty. No squeal/hiss so far. I seemed to have developed a crackling scratchy volpot on the guitar. This is new pot and it did not do this prior to me opening amp up. Could this be amp issue? Or do I have to open guitar up? Have a great weekend folks.
-
Does the tone stack, input wires or wire going from pin 7 of 12ax7 have anything to do with the voltage going to V1?
-
Does the tone stack, input wires or wire going from pin 7 of 12ax7 have anything to do with the voltage going to V1?
I'm sorry but I don't understand what your asking??????
Brad :dontknow:
-
The genius who built my amp built a 5F2. I asked for a 5F2-A. I re did it to 5F2-A specs and voltage went from 167 on 12ax7 to 198V.
-
The genius who built my amp built a 5F2. I asked for a 5F2-A. I re did it to 5F2-A specs and voltage went from 167 on 12ax7 to 198V.
:laugh:
You did good, you figured it out and fixed it.
Hey, so he forgot the -A. It's just a suffix.
Brad :l2: