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snarlin' Pro-Reverb

:

8/29/1999 10:16 AM

snarlin' Pro-Reverb

any ideas on this phenonmena? A BF Pro-Reverb

that sometimes launches into a loud "snarling,

wailing, screaming" sorta feedback sounding, maybe

even an ocscillation type of sound. ONLY occurs

at hi signal operation, like Volume on 8 and

a strong lick or chord played. I have thought

of pre-amp tube overload but the howling sound

is more like oscillations/feedback.

preamp tube is a Phillips/Made in England(Mullard)

and is really strong, output tubes are yellow base-labeled

Sylvanias..... and nearly EVERY component on this

amp has been recently replaced-from pwr sup filter caps

to output tubes screen and grid resistors.

Any ideas/suggestions? thanks mucho for any thoughts !

8/29/1999 7:59 PM

Jeff:

I don't know if this will help, but you might try splitting up the common cathode resistors and Ck bypass caps (double the value of the resistor and optionally cut the capacitance in half). And double check all of your cathode ground connections.

My 65 Pro used to make this sound almost like "indigestion" right after I'd play it fast and loud- like the tide going in and out, or water sloshing around in a bucket. It wasn't a loud noise, but more like the background noise you might hear from a phaser or flanger. (I think it still might do that because the one thing I haven't changed yet is the filter caps.)

Steve Ahola

8/30/1999 6:14 AM

Jeff;

Here's a possible solution. You might have a severely microphonic preamp tube. Turn the amp up to the volume where it starts the howling and then go in the back and tap your tubes with the end of a pencil. If one is bad the tapping should set off some nasty oscillation. A while back I had retubed a BF Super with a full rack of Phillips tubes and after about 2 weeks every d**n one went microphonic. Uncle Ned over at triode had said that they got a few lots in that were no good so it's worth taking a look.

The first thing you always want to check is the tubes! Even if they're new. Sometimes they can go south for no apparent reason.

Regards;

Carl Z

Summit Amps

8/30/1999 10:03 AM
jeff	Thanks Steve & Carl. I suspect the pre-amp tubes .. Phillips & NOS non-withstanding ..still can go or be bad, especially since I have already replaced all caps in this amp. p.s Good description of the 'noise' Steve, that's exactly how it sounds- with a feedback sorta' loop to keep the annoyance going!

8/30/1999 6:06 PM

well is was not the tube. tried several known good tubes

but i have determined this: If i gently wiggle the tube

in question (12ax7 for Vib ch), all hell breaks loose..

e.g. LOUD popping snarly noises.. and ... that same

sorta feedback type loud hum thru the speaker.

I suspect either 1. a crappy tube socket (current socket

is a cinch, pins are tensioned properly and socket

"look" ok, or (2.) one or more pin connections on this

tube are bad .....

since resoldering each pin connection is 'bout half the work

of replacing the socket .. whadda you guys think?

8/31/1999 3:18 AM
Tim C.	Jeff, Have you tried cleaning the tube sockets with a non lubricating cleaner such as "Blue Shower"? Spray the sockets and then place the tubes in and out of the sockets about 5 times each. Just a thought. Tim C.

8/31/1999 3:21 AM
Tim C.	Jeff, Additional: I should have said to only clean the pre amp tube sockets. Do Not clean the power tube sockets that way. If you do, make sure the sockets are completely dry before replacing the power tubes. I have used a hair dryer to speed the process at times. Tim C.

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