Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: worth on August 21, 2010, 09:49:03 am

Title: Showman/6G16 trem ?
Post by: worth on August 21, 2010, 09:49:03 am

Any reason the 6G16 type bias modulation trem wouldn't work well in a 4 - 6L6 Fender ? I ask because I did this trem mod to my '68 Showman. It worked for about 2 weeks , then quit..... still searching for the cause.

Title: Re: Showman/6G16 trem ?
Post by: 6G6 on August 21, 2010, 10:06:46 am

If it worked for two weeks, then it can work.

I would look at what could have changed.
Maybe a small crack in a solder joint, that made contact for a while,
then just looked like it should be OK, after that.

Title: Re: Showman/6G16 trem ?
Post by: worth on August 21, 2010, 11:12:34 am

I've chopsticked , reflowed solder , changed 12AX7 , checked resistance on the intensity pot. All resistors in the trem circuit are new carbon film. Haven't checked resistance on the speed pot though. The Showman sounds great , but not a sound from the trem.

Title: Re: Showman/6G16 trem ?
Post by: sluckey on August 21, 2010, 12:38:38 pm

Verify the oscillator is working and readjust the bias.

Title: Re: Showman/6G16 trem ?
Post by: tubeswell on August 21, 2010, 03:37:34 pm

I know this is a dumb question, but did you change the oscillator tube?

Title: Re: Showman/6G16 trem ?
Post by: worth on August 21, 2010, 09:52:51 pm

Yes , the first thing I did was to try another 12AX7.

Title: Re: Showman/6G16 trem ?
Post by: tubeswell on August 22, 2010, 05:09:31 am

Okay, what are the idle voltages like on the oscillator tube pins? (not the filament pins)

Title: Re: Showman/6G16 trem ?
Post by: sluckey on August 22, 2010, 07:25:38 am

What voltages do you measure? When the osc is working the voltages will all be fluctuating at the trem speed. If using a digital meter to read voltages the readings will just look crazy and always changing. If the osc is not working, the voltages will be steady.

Title: Re: Showman/6G16 trem ?
Post by: worth on August 22, 2010, 10:28:52 am

I found the problem.... no voltage on pin 2 of the trem tube. I ran a jumper from pin 2 to the connection on the board and the trem came to life.

Title: Re: Showman/6G16 trem ?
Post by: worth on August 22, 2010, 01:35:41 pm

I also added a 1N4007 diode across the intensity pot..... increased the trem intensity.