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Post subject: Re: 1967 Vibro Champ Issue
Posted: Wed Nov 22, 2017 9:20 am
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BMW2002Ti wrote:
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:


Thanks, my parts should be in this weekend, I will definitely start with the 6v6 cathode resistor and cap, the 1K and 10K. I ordered enough other parts to then, if the problem persists, start lifting, evaluating, and, change if needed, I will definitely lift and evaluate the 100K on the plate load resistors, as they can produce crackle noises in the amp
Thank you, and have yourself a wonderful Thanksgiving
mud


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Post subject: Re: 1967 Vibro Champ Issue
Posted: Sat Nov 25, 2017 9:26 am
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Friday when I got home my parts were in and after I changed the cathode cap and resistor, it all sounded normal again no more trailing of sound when turning on or off
Image
Was this a good place for the metal oxide, I am debating with my self if I should use the CC in there, I haven't done much in the way of evaluating the other resistors and caps, between family stuff and getting playing time in over this holiday weekend time just goes fast. I will get to it as things slow up
Thank you all for your help, have a nice weekend
mud


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Post subject: Re: 1967 Vibro Champ Issue
Posted: Sat Nov 25, 2017 10:36 am
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That's great that you got that problem nailed. The oxide resistor is fine. Whatever noise it creates is not in the series signal path.
Now, I couldn't help but notice that the phillips screw next to it looks a half turn loose.....
Have a good weekend.


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Post subject: Re: 1967 Vibro Champ Issue
Posted: Sat Nov 25, 2017 9:37 pm
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TimsAudio wrote:
That's great that you got that problem nailed. The oxide resistor is fine. Whatever noise it creates is not in the series signal path.
Now, I couldn't help but notice that the phillips screw next to it looks a half turn loose.....
Have a good weekend.

Thanks, I put a screw driver to it, but it was tight, I did some evaluating today and found one 100K on the plate giving 118K so being it was more than 10% I changed it, and some hiss went away
mud


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Post subject: Re: 1967 Vibro Champ Issue
Posted: Sun Nov 26, 2017 10:09 am
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Carbon comp or metal film?
Which position?


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Post subject: Re: 1967 Vibro Champ Issue
Posted: Tue Nov 28, 2017 2:45 pm
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TimsAudio wrote:
Carbon comp or metal film?
Which position?


I put the metal oxide with the bypass cap for the 6v6 and put the CC for the 100K plate resistor, I do have a 470 ohm 2 watt for the bypass I could use instead of the metal oxide
mud


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Post subject: Re: 1967 Vibro Champ Issue
Posted: Tue Nov 28, 2017 5:18 pm
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Metal oxide are better for the cathode resistor (IMHO). Better stability over time, esp if heat is a concern. I like non-inductive wire-wound Mills or Ohmite resistors in this position and also in the power rail --- as an even more overkill. But, you must realize I get a perverse thrill out of knowing some tech will open up the amp and see those resistors in perfect tolerance --- 50 years from now. :)

I like to run higher voltage bypass caps in output stages. They tolerate heat better.

I think I used a precise flameproof Vishay resistor in the cathode position. F&T 33mfd/160VDC bypass cap.

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Post subject: Re: 1967 Vibro Champ Issue
Posted: Thu Nov 30, 2017 2:06 pm
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BMW2002Ti wrote:
Metal oxide are better for the cathode resistor (IMHO). Better stability over time, esp if heat is a concern. I like non-inductive wire-wound Mills or Ohmite resistors in this position and also in the power rail --- as an even more overkill. But, you must realize I get a perverse thrill out of knowing some tech will open up the amp and see those resistors in perfect tolerance --- 50 years from now. :)

I like to run higher voltage bypass caps in output stages. They tolerate heat better.

I think I used a precise flameproof Vishay resistor in the cathode position. F&T 33mfd/160VDC bypass cap.

Image

But, you must realize I get a perverse thrill out of knowing some tech will open up the amp and see those resistors in perfect tolerance --- 50 years from now. :) :lol:
I see you have used the Jupiter Vintage Tone cap, how do you like it ?, and did you change out the mid and bass cap, if so were they out of value or do these have better tone.
mud


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Post subject: Re: 1967 Vibro Champ Issue
Posted: Thu Nov 30, 2017 7:09 pm
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For this amp (1964 VC) --- I played with a bunch of coupling cap combinations, I happen to have in stock. I liked the NOS Mallory, NOS Sprague 6PS (USA) in those positions (0.1 and 0.47mfd caps) --- best clean tone, IMHO. The Jupiter yellow Vintage tone is a very nice cap. Used them in several SR, Vibrolux Reverb, and Bassman amps with good success.

I changed the VIBRATO section disc cap with 1KV rated Sprague I had. And replaced the 250 pico-farad cap in the treble section with a silver mica cap (same value).

Some resistors were changed (using 10% NOS A-B). The cathode cap on the input stage is a Mills 5-watt.

I've played this amp at "10" for hours. It's a very good, stable amp (so far). Running RCA 5Y3GT & 6V6GT. TFK ECC83 tubes. Weber 8-inch 8F125.

:mrgreen:


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