How to take voltage readings ? Tweed Princeton

[Boone]

Will do Sluckey, I will take reading again after its replaced and post results. How do I test the cap near the 12ax7?

[Boone]

How many volts should read at the lifted lead with a good cap in there?

[Willabe]

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.

 

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             

[Boone]

I have a couple of new Jupiter type mustards . They have black line at one end: should line go toward 12ax or input jacks?

[Willabe]

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         

[Boone]

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.

[Willabe]

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    

[HotBluePlates]

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.

[Willabe]

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     

[Willabe]

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      

[Willabe]

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


             Brad      

[Boone]

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.

[sluckey]

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.

[Boone]

Swapped caps: 4.5 -6.7 mV at pin 5 . Reading is swinging up down and back btw these figures. Tube still red plating.

[Boone]

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!

[Willabe]

I knew Hubert. I can't say we were really friends but he knew would recognize me and sometimes remembered my name.  

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.    

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.    

Then I picked up my guitar and smelled it. WOOW! It was from that cigar Hubert was smoking!    

Got out the lemon Pledge and drowned it 2/3 times and it was pretty good but it still lingered in the strings.    


               Brad        

[Boone]

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?

[punkykatt]

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

[Willabe]

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.    

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.  


            Brad      

[labb]

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.

[sluckey]

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.

[Boone]

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

[labb]

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.

[sluckey]

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.

[labb]

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.

[punkykatt]

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.

[Boone]

#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?

[sluckey]

#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.

[Boone]

Thank you everybody! I would say 'well done' to you folks. I will swap out the cathode res this evening,recalculate and post results.

[Boone]

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.

[Boone]

Anyone know to attach pics to this thread? After res swap- major noise issues with vol/tone maxed.

[Boone]

I think I figured the photo thing out. Will post pic later.

[Willabe]

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    

[Boone]

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

[sluckey]

If you want a Princeton, I highly recommend you replace that little Silvertone OT with a tougher one.

[HotBluePlates]

... 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.

[Boone]

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.. ....

[Boone]

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.

[Willabe]

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    

[Boone]

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?

[Willabe]

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      

[Boone]

I will do that and post back tomorrow with 680 installed. Thank you.  Boone

[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.

[Boone]

Does the tone stack, input wires or wire going from pin 7 of 12ax7 have anything to do with the voltage going to V1?

[Willabe]

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     

[Boone]

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.

[Willabe]

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.

 

You did good, you figured it out and fixed it.

Hey, so he forgot the -A. It's just a suffix.


             Brad