Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: centervolume on May 14, 2019, 08:23:17 pm

Title: Dead Channel: 1960 5G5 Pro Amp
Post by: centervolume on May 14, 2019, 08:23:17 pm

Gents and others

The normal channel on my gramplifier has done stopped with it's amplifyin ways... no nothin! Vibrato channel is working fine.

I checked the tube and replaced with 'known good'; checked the plates and they are receiving the necessary approx. 180vdc.

I checked for broken solder joints and suppose I could reflow the works. I used the probe to conduct a pop test on grid and plate lines and that revealed some weaker or dead areas so I feel like I'm able to narrow down the culprit but still feel as if I'm in the dark.

Is there anything like a standard approach or work flow progression I can adopt for this somewhat common situation?

https://images.app.goo.gl/dsDRRd8zFHsjZPuu9

https://images.app.goo.gl/dsDRRd8zFHsjZPuu9 (https://images.app.goo.gl/dsDRRd8zFHsjZPuu9)

This model has the tone stack mounted up on the pots

Title: Re: Dead Channel: 1960 5G5 Pro Amp
Post by: sluckey on May 14, 2019, 08:59:06 pm

Check voltages for all tube pins. Compare to schematic.

Your topic says 5G5 but your links are to a 6G5 schematic. Why???

Title: Re: Dead Channel: 1960 5G5 Pro Amp
Post by: shooter on May 15, 2019, 08:30:11 am

Get the #'s Sluckey asked for;
fwiw
I had similar problem on 66 super, signal got lost in the TS after input tube, for $12 +shipping I replaced TS & gain pots, 2 caps, and put a spacer between the eyelet and backer board. satisfied customer  :laugh:

Title: Re: Dead Channel: 1960 5G5 Pro Amp
Post by: centervolume on May 15, 2019, 03:16:10 pm

Ok - so 6g5 is printed on schematic and 5g5 is printed on tube chart. It’s a record keeping hiccup found with very first brown amps straightened out by the end of 1960. In short, aside from the usual tinkering, the amp I am working on is the same (5 preamp tube) amp as is printed on the schematic.

Voltages

V1
Pin 1: 194
Pin 2: -
Pin 3: 1.39

Pin 6: 188
Pin 7: -
Pin 8: 1.39

V2

Pin 1: 75 (plate load resistor ok)
Pin 2: -
Pin 3: 1.5

Pin 6: 269
Pin 7: -
Pin 8: 1.5

V3
Pin 1: 130-180 oscillating
Pin 2: -
Pin 3: -

Pin 6: 242
Pin 7: -
Pin 8: 1.39

V4

Pin 1: 262
Pin 2: .06
Pin 3: 14.4

Pin 6: 231
Pin 7: .1
Pin 8: 14.4

V5
Pin 1: 350
Pin 2: 20
Pin 3: 30

Pin 6: 326
Pin 7: 21
Pin 8: 30

Title: Re: Dead Channel: 1960 5G5 Pro Amp
Post by: centervolume on May 15, 2019, 03:22:41 pm

Ok my bad - I had a 5965 in V2

Wish I could blame it on the dog or whatever

Sovtek 7025 and she’s up and running

Thanks - the voltage chart first approach is a winner