Phonoland

When you first fire her up, the volume is sometimes very loud, it will get to normal after a couple of seconds then go loud and vacillate for a minute or so. It only occurs on start up. Doesn't always occur and always levels out to normal after about a minute.

I had the amp rebuilt about 8 months ago. At that time, it was converted to use a ceramic cartridge. I have since replaced it with a magnetic, so the output from the cartridge goes to a phono preamp prior to going into the amp. At the time it was rebuilt, the person doing the work also bypassed the auto level functionality (I know that there are mixed feelings on this one). So the question is what is the most likely culprit? Am I dealing with a bad tube that is fine after it heats up? Or perhaps a trace that expands or maybe an issue with the pot that is fine when heated up or something else?

Thanks
Brooks

I remember the discussion. First, is the 12AU7 still in place? Half of that tube is the AGC reactance control. The other half was the Cobra oscillator. If AGC was eliminated then neither should be necessary and the tube removed.

If it is there the rebuilder might have kept some form of fade-up (squelch) at the beginning of each record and the problem you are experiencing is either a poor connection on the mute/squelch contacts on the Mute-Play switch (near motor) or the the 12AU7 tube itself.

You can see the position of the tubes on the printer board here: http://www.verntisdale.com/schem/532.jpg

Other tubes and components can cause this sort of thing but, in general the area of greatest control of the level is the former AGC ckt.

Rob

When Bill did his work on the amp it eliminated the need for the 12au7 and one of the 12AX7 tubes

Hi Goat--
Just curious--why don't you contact "Bill" about this ??
Ron Rich

Ron Rich wrote:Hi Goat--
Just curious--why don't you contact "Bill" about this ??
Ron Rich

Definitely can, y'all have just become my first stop for all things jukebox. So more force of habit than anything else, plus you always seem to have the answer.
Brooks

Hi Goat,
OK--fair enough--By any chance, did you read my "Attn Newbies" above ?? Your question is the same as my Aunt's--
un-answerable as I do not have enough info- Ron Rich

Brooks, if the AGC was completely removed as you describe, there should not be anything to cause volume variation. What level comes up at first should stay and not go down. So, if at all possible, try replacing the small tubes on the board.. One may be gassy or have a hot spot.

Rob

Rob-NYC wrote:Brooks, if the AGC was completely removed as you describe, there should not be anything to cause volume variation. What level comes up at first should stay and not go down. So, if at all possible, try replacing the small tubes on the board.. One may be gassy or have a hot spot.

Rob

I reached out to Bill Bickers and he had the same thought. Specifically, he implicated the 12AX7. I replaced it and everything works fine. So I'll consider the problem solved. Hopefully, someone will benefit from it in the future.

On a sidenote, I'm thinking I may get a spare set of tubes. Any thoughts/advice on that front? Get full set or just some? Get from E-bay? Specific brands to get or avoid?
Thanks
Brooks

When the need arises, I replace the tubes in my customer's sets with N.O.S. replacements.
They may cost a bit more, but I tend to find that in numerous occasions they perform better, tolerate abuse better, and eliminate callbacks.
RCA, GE, Sylvania, etc... all can't be beat.

MattTech wrote:When the need arises, I replace the tubes in my customer's sets with N.O.S. replacements.
They may cost a bit more, but I tend to find that in numerous occasions they perform better, tolerate abuse better, and eliminate callbacks.
RCA, GE, Sylvania, etc... all can't be beat.

Thanks

Goat,
A tube supplier I use is listed above-- in New-Used parts----" Ron Rich