It is currently Mon Mar 16, 2020 9:04 am

All times are UTC - 7 hours



Post new topic Reply to topic  [ 84 posts ]  Go to page Previous  1, 2, 3, 4, 5, 6  Next
Go to page Previous  1, 2, 3, 4, 5, 6  Next
Author Message
Post subject: Re: 1967 Vibro Champ Issue
Posted: Tue Nov 14, 2017 9:29 am
Offline
Professional Musician
Professional Musician

Joined: Thu Aug 07, 2014 3:25 pm
Posts: 1023
If you can tickle pin 6 and make the same crackle, you've found the problem. Bad solder or a bad socket pin, maybe a bad plate resistor.
I would reflow the solder on the socket.
Good Luck.


Top
Profile
Fender Play Winter Sale 2020
Post subject: Re: 1967 Vibro Champ Issue
Posted: Tue Nov 14, 2017 12:34 pm
Offline
Professional Musician
Professional Musician

Joined: Wed Dec 15, 2010 7:06 am
Posts: 1662
TimsAudio wrote:
If you can tickle pin 6 and make the same crackle, you've found the problem. Bad solder or a bad socket pin, maybe a bad plate resistor.
I would reflow the solder on the socket.
Good Luck.

TimsAudio thanks, so I touch pin 6, I do get crackle, following the pin 6 lead to the leg of the .02 coupling cap, I also get the same crackle, should I be looking at the 100K load resistor than, I did retention and cleaned the socket pins
mud


Top
Profile
Post subject: Re: 1967 Vibro Champ Issue
Posted: Tue Nov 14, 2017 12:36 pm
Offline
Professional Musician
Professional Musician

Joined: Wed Dec 15, 2010 7:06 am
Posts: 1662
BMW2002Ti wrote:
Check all resistors and solder points. Including that resistor strapped across pins 1 & 6 of V2. Because of the tight area of these sort of connections --- the factory something can't make a completely good solder. I had a couple amps where small cracks develop in these inner-socket connections, over time (sometimes many years).

Good hunting!

http://www.electronicstudio.net/schemat ... layout.pdf


I compressed air all of the resistors and did not change a thing, maybe I need to get the below zero spay or is it just compressed air
mud


Top
Profile
Post subject: Re: 1967 Vibro Champ Issue
Posted: Tue Nov 14, 2017 12:38 pm
Offline
Professional Musician
Professional Musician

Joined: Wed Dec 15, 2010 7:06 am
Posts: 1662
sfceric64 wrote:
Haven't been around for a while, a 3k resistor in the first stage of the PSU rail will help drop your voltages from the screens of the output through to the 12ax7's. The only thing it wont do is drop the plate voltage and what your 5y3 is seeing from the power transformer. It might help some to preserve the original characteristics of the amp but many prefer to just keep it original. Again, I like to use the brown box in order to adjust the input voltages. just sayin.


I have been giving this box some thought
mud


Top
Profile
Post subject: Re: 1967 Vibro Champ Issue
Posted: Tue Nov 14, 2017 3:18 pm
Offline
Professional Musician
Professional Musician

Joined: Wed Dec 15, 2010 7:06 am
Posts: 1662
OK let me kind of recap ( no pun intended )
1) I cleaned and retention all the tube sockets
2) Sprayed compressed air on all resistors, one at a time and played guitar after every one no change
3) Changed all 4 tubes and had same results with tubes that were in place
4) Clipped the leads of the 1st preamp stage Cathode bypass capacitor When I did this I played some guitar and it sounded chocked up I assume the 12AX7 was starving for electrons and I hoping this was alright to do
5) Noticed crackling when probing pin 6 of the preamp 12AX7, and same crackling when probing where pin 6 lead goes to leg of .02 coupling cap.
So here is what had changed and what is happening now:
After I clipped the cathode cap and the sound of my guitar was low and not pleasant I turned all off than uncliped the leads turned it back on no crackle sound I played my guitar and it sounded OK turned off the amp no crackle fad out, turned amp back on no sound, ate some dinner. After about 45 minutes to an hour turned up the volume and it sounded bad. I have to describe it as compressed, if I play soft it seem almost right, but than when I strum heavy the sound at first hits is low and compressed than volume raise and compresses again does this until the strings settle to fad out. Sounds like a compressor on, and than bypassed, back on, and than bypassed until the strings settle, similar to when I clipped the leads on the 1st stage cathode cap
So what is my next move:
TimsAudio wrote:
If you can tickle pin 6 and make the same crackle, you've found the problem. Bad solder or a bad socket pin,would this travel to .02 coupling cap ? maybe a bad plate resistor. should I lift a leg and check it's value, I do not believe I can clip across it and be accurate, or do I lift both legs
I would reflow the solder on the socket.
Good Luck.

Should I start with lifting 1st stage cathode checking it's value or should I just get 3x 25uf 50v and 1x 10uf and put in new, and after that do I start lifting resistors and evaluate,
mud


Top
Profile
Post subject: Re: 1967 Vibro Champ Issue
Posted: Tue Nov 14, 2017 6:29 pm
Offline
Professional Musician
Professional Musician

Joined: Thu Aug 07, 2014 3:25 pm
Posts: 1023
Its ok to play with the cathode clipped. It will sound funny when you do a lot of circuit hacks for testing.
You can clip or short components in the ac domain.
Don't try it with plate voltages.
The preamp distortion you describe after warmup is significant.
The 1.5k cathode resistor controls the dc operating point of the 12ax7. If it drifts upward, it upsets the dc balance. This causes early clipping and distorts when you dig in to the strings.
Perhaps the intervention with the clip lead disturbed the resistor enough to change the symptom a bit. The resistor deserves a closer look.
Certainly pulling a leg of a component gives you a chance to measure a component. But the other thing it does is to allow substitution.
You can tack solder substitute components into the circuit you just disconnected.
For many substitution situations, you may not have the exact value in your inventory. In this case you might use a value drift from 820 to 3.3k ohms. Sure, it may sound funny, but if the crackle goes away, you've nailed it.
You can tack solder a new plate resistor on pin 6 if you lift one leg of the original.
Even the .02 coupling cap can be substituted to eliminate that possibility.
While these techniques are messy, i use a lot of substitution and eliminating because meters aren't up to the task of spotting intermittent problems.
The time spent soldering in used parts or jumpering sections is less than logical diagnosis with meters.
Its more fun too.


Top
Profile
Post subject: Re: 1967 Vibro Champ Issue
Posted: Wed Nov 15, 2017 10:14 am
Offline
Professional Musician
Professional Musician

Joined: Tue Nov 27, 2012 6:56 am
Posts: 1677
Location: Coastal Bend, Tx.
Quote:
Should I start with lifting 1st stage cathode checking it's value or should I just get 3x 25uf 50v and 1x 10uf and put in new, and after that do I start lifting resistors and evaluate,
mud
That's what I would do w/ the electro-caps, working from V1 to the output. Using the lift and sub approach, if your trying to preserve the original aspects.
Considering you already checked cap leak, tubes, and resistors.


Top
Profile
Post subject: Re: 1967 Vibro Champ Issue
Posted: Wed Nov 15, 2017 6:50 pm
Offline
Professional Musician
Professional Musician

Joined: Wed Dec 15, 2010 7:06 am
Posts: 1662
BMW2002Ti wrote:
Check all resistors and solder points. Including that resistor strapped across pins 1 & 6 of V2. Because of the tight area of these sort of connections --- the factory something can't make a completely good solder. I had a couple amps where small cracks develop in these inner-socket connections, over time (sometimes many years).

Good hunting!

http://www.electronicstudio.net/schemat ... layout.pdf
sfceric64 wrote:
Quote:
Should I start with lifting 1st stage cathode checking it's value or should I just get 3x 25uf 50v and 1x 10uf and put in new, and after that do I start lifting resistors and evaluate,
mud
That's what I would do w/ the electro-caps, working from V1 to the output. Using the lift and sub approach, if your trying to preserve the original aspects.
Considering you already checked cap leak, tubes, and resistors.
TimsAudio wrote:
Its ok to play with the cathode clipped. It will sound funny when you do a lot of circuit hacks for testing.
You can clip or short components in the ac domain.
Don't try it with plate voltages.
The preamp distortion you describe after warmup is significant.
The 1.5k cathode resistor controls the dc operating point of the 12ax7. If it drifts upward, it upsets the dc balance. This causes early clipping and distorts when you dig in to the strings.
Perhaps the intervention with the clip lead disturbed the resistor enough to change the symptom a bit. The resistor deserves a closer look.
Certainly pulling a leg of a component gives you a chance to measure a component. But the other thing it does is to allow substitution.
You can tack solder substitute components into the circuit you just disconnected.
For many substitution situations, you may not have the exact value in your inventory. In this case you might use a value drift from 820 to 3.3k ohms. Sure, it may sound funny, but if the crackle goes away, you've nailed it.
You can tack solder a new plate resistor on pin 6 if you lift one leg of the original.
Even the .02 coupling cap can be substituted to eliminate that possibility.
While these techniques are messy, i use a lot of substitution and eliminating because meters aren't up to the task of spotting intermittent problems.
The time spent soldering in used parts or jumpering sections is less than logical diagnosis with meters.
Its more fun too.

TimsAudio
Thanks for these wonderful tips, and I am having a lot of fun. I have always had a knack for systems, and this amp electronics I find to be just another system, once you figure out the language, and the road maps, and learn some of the tricks, it makes a lot of sense

I did come across an issue and can not go any further until I get parts. What I found was the the power amp cathode cap had continuity, that's how I found it in the circuit, I extracted it and meter it on my fluke 175 and it was dead. The 470 1watt resistor metered 736 ohms. I do not know if this was the issue from the start, but I need to fix first

sfceric64 Thanks, while I am waiting for parts I guess it a good time to start the lifting and evaluating
BMW2002Ti Thanks for all the time you have spent on my VC helping.
stratele52 Thanks for your time

I most likely would have brought it to the tech that has worked on some of my amps if it weren't for this forum, you forum members have been so helpful, I can't thank you enough.
I do have another question about parts: I think I should have parts being I own a SR and VC. I don't want to buy a part, wait for it, find out I need something else and wait again, and spend more money on shipping than the actual parts so I put together a parts list.
Should I get a certain brand I see These Sprauge Atom TVA 1306 everywhere for the 25uf or are there other brands I should be looking at. The 10uf 25 VDC do I use this value for the 2nd preamp stage cathode pin 8 on 12AX7 or do I use a 25uf 50VDC as I see being used quite common these days.
On to resistors should I use a certain type: Carbon Composition, Metal Film, Carbon Film, and Metal, Oxide Film resistor
Any suggestions of where to purchase these items in one place would be very handy
My shopping list and I hope the resistors come in packs of 5
25 uF at 50 Volts "Sprague Atom TVA 1306 Tubular Axial Electroltyic Capacitor"
10 uF at 25 Volts Axial
470 ohm 1W
1.0K ohm 2W
10K ohm 2W
68 ohm 1/2W
1.5K ohm 1/2W
2.7K ohm 1/2W
4.7K ohm 1/2W
100K ohm 1/2W
220K ohm 1/2W
1.0M ohm 1/2W
Thanks again
mud


Top
Profile
Post subject: Re: 1967 Vibro Champ Issue
Posted: Thu Nov 16, 2017 9:39 am
Offline
Professional Musician
Professional Musician

Joined: Thu Aug 07, 2014 3:25 pm
Posts: 1023
Sprague caps for the cathodes is THE choice.
Power resistors should be metal oxide.
Signal path resistors should be metal film.
Plate resistors can be carbon comp if you like the vintage sizzle.
when you mount the new cap and 470, get a little distance between them to avoid overheating the cap.


Top
Profile
Post subject: Re: 1967 Vibro Champ Issue
Posted: Thu Nov 16, 2017 10:26 am
Offline
Professional Musician
Professional Musician

Joined: Wed Dec 15, 2010 7:06 am
Posts: 1662
TimsAudio wrote:
Sprague caps for the cathodes is THE choice.
Power resistors should be metal oxide.
Signal path resistors should be metal film.
Plate resistors can be carbon comp if you like the vintage sizzle.
when you mount the new cap and 470, get a little distance between them to avoid overheating the cap.


Oh thank you,
I can now put together my order. I do want that vintage sizzle
mud


Top
Profile
Post subject: Re: 1967 Vibro Champ Issue
Posted: Thu Nov 16, 2017 1:59 pm
Offline
Rock Star
Rock Star
User avatar

Joined: Sat Jul 03, 2010 2:18 pm
Posts: 6544
I try to keep CC resistors in the signal path. Just for vintage tone sake.

However, from what I've learned... CC resistors are only really critical as grid stoppers and grid-to-ground resistors --- due to their inherit low-inductive character. Plus, somewhat limited bandwidth. This helps to keep ultrasonic instabilities to a minimum. I presume a low-inductive WW resistor will work fine. I use WW, 5-watt ones as screen resistors, because of their stability, long-life... under heated conditions (the socket).

Areas where heat or high current load is an issue, metal oxide and wire-wound resistors are superior. MO will last and not drift around like a typical CC one.

It's getting hard to find good CC resistors. Carbon film, yes. Carbon comp, no. I just happen to have a large stash of Allen-Bradley CC resistors sitting in a cool, dry place --- waiting for future use.


:mrgreen:


Top
Profile
Post subject: Re: 1967 Vibro Champ Issue
Posted: Thu Nov 16, 2017 2:45 pm
Offline
Professional Musician
Professional Musician

Joined: Tue Nov 27, 2012 6:56 am
Posts: 1677
Location: Coastal Bend, Tx.
Right on what Tim said.
If your gonna place a biggish order, AES or Mouser are good bets to have all the components your looking for.
If you wanna shop Ebay, New Old Sounds is pretty solid but may not have all the components your looking for.
Maybe consider that 3k 2or3 watt 1st stage PSU resistor I mentioned to help lower the VDC from the screen grids of the output through to the 12ax7s.
I like the 10uv x 25v in stage 2.


Top
Profile
Post subject: Re: 1967 Vibro Champ Issue
Posted: Fri Nov 17, 2017 11:34 am
Offline
Professional Musician
Professional Musician

Joined: Wed Dec 15, 2010 7:06 am
Posts: 1662
BMW2002Ti wrote:
I try to keep CC resistors in the signal path. Just for vintage tone sake.

However, from what I've learned... CC resistors are only really critical as grid stoppers and grid-to-ground resistors --- due to their inherit low-inductive character. Plus, somewhat limited bandwidth. This helps to keep ultrasonic instabilities to a minimum. I presume a low-inductive WW resistor will work fine. I use WW, 5-watt ones as screen resistors, because of their stability, long-life... under heated conditions (the socket).

Areas where heat or high current load is an issue, metal oxide and wire-wound resistors are superior. MO will last and not drift around like a typical CC one.

It's getting hard to find good CC resistors. Carbon film, yes. Carbon comp, no. I just happen to have a large stash of Allen-Bradley CC resistors sitting in a cool, dry place --- waiting for future use.


:mrgreen:


Well I am a little crazy right now, as making a discussion is never easy, and hours of research, just goes on and on, but that's me, somethings never change.
I do not have any AB's in my possession and last night after spending a couple of hours looking for AB's I decide I will just keep my eyes open for them in the future
I decided as of now to go with the CC's except for the power rail I will use Metal Oxide, and for the 470 ohm 1w for the power amp cathode resistor
Thanks for all the help
mud


Top
Profile
Post subject: Re: 1967 Vibro Champ Issue
Posted: Fri Nov 17, 2017 11:43 am
Offline
Professional Musician
Professional Musician

Joined: Wed Dec 15, 2010 7:06 am
Posts: 1662
sfceric64 wrote:
Right on what Tim said.
If your gonna place a biggish order, AES or Mouser are good bets to have all the components your looking for.
If you wanna shop Ebay, New Old Sounds is pretty solid but may not have all the components your looking for.
Maybe consider that 3k 2or3 watt 1st stage PSU resistor I mentioned to help lower the VDC from the screen grids of the output through to the 12ax7s.
I like the 10uv x 25v in stage 2.

I am going to stick with 10uf 25v. I am using AES for now it's easier to navigate, Mouser too many choices for the same item, I will need to spend some time there.
I am ordering a 1K 2 watt, and a 3K 2 watt to experiment with
thanks for the help
mud


Top
Profile
Post subject: Re: 1967 Vibro Champ Issue
Posted: Wed Nov 22, 2017 8:49 am
Offline
Rock Star
Rock Star
User avatar

Joined: Sat Jul 03, 2010 2:18 pm
Posts: 6544
Looks like you are re-building most of the amp --- except for the irons. I've redone quite a few VC and Champs. They are hot items. Well worth the proper restoration effort.

IMHO, the power supply is most important. Followed by the cathode resistor and bypass cap on that 6V6GT tube. Good quality parts and proper placement really helps.

Good luck! And Happy Turkey Day!

:mrgreen:


Top
Profile
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 84 posts ]  Go to page Previous  1, 2, 3, 4, 5, 6  Next
Go to page Previous  1, 2, 3, 4, 5, 6  Next

All times are UTC - 7 hours

Fender Play Winter Sale 2020

Who is online

Users browsing this forum: No registered users and 1 guest


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum

Search for:
Jump to: