Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: jacodaro on December 31, 2018, 02:29:25 pm

Title: Ampeg V-2
Post by: jacodaro on December 31, 2018, 02:29:25 pm

1973, modded for 6550 tubes years ago. Original filter caps but no power supply noise.
The problem: distorted sound in both channels, similar to over biased power tubes, until the amp warms up for five minutes. Then it's loud and clean. Any ideas before I open the amp up? Thanks.

Title: Re: Ampeg V-2
Post by: shooter on December 31, 2018, 07:44:30 pm

Quote

warms up for five minutes.

that's the normal start up for most of the RF amps I worked on, but guitar ones.....
clip your meter on the DC power rail n see if it's the rail that's slow or a tube(s) that's cranky

Title: Re: Ampeg V-2
Post by: jacodaro on January 04, 2019, 11:37:31 pm

I checked all voltages as soon as I place standby into run mode, and all voltages are there immediately and correct. One thing is that if I turn standby to run soon after turning on it never warms up and continues to distort. I have to leave it on standby for 5 min from turn on before it cleans up. Now here's where it really gets screwy. If I a run another amp from the "ext amp" jack (from the 1st 1/2 of 12dw7) the sound is clear from the 2nd amp, but also now clean from the V2 speaker out. Unplug the ext amp out, or turn the 2nd amp volume down? And the output from V2 is distorted. The "ext amp" out is a non-shorting jack that originates from the same point as the feed to the PI. Why would it make any difference to the V2 power amp?  I usually track this stuff down pretty quick. I'm stumped. Thanks for any help offered.

Title: Re: Ampeg V-2
Post by: jacodaro on January 10, 2019, 06:15:09 pm

I think I got this. Found 4.60 VAC on the first stage filter caps/power tube plates. And there is power supply hum.

Title: Re: Ampeg V-2
Post by: sluckey on January 10, 2019, 07:02:47 pm

Quote from: jacodaro on January 10, 2019, 06:15:09 pm

I think I got this. Found 4.60 VAC on the first stage filter caps/power tube plates. And there is power supply hum.

That's pretty typical for that much ripple at the first filter cap.

Title: Re: Ampeg V-2
Post by: jacodaro on January 11, 2019, 06:01:16 pm

Resolved. The second set of power tubes also had a bad tube. Third set and all is good. Thanks.