Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: oogabooga23 on October 24, 2022, 09:31:43 pm

Title: St George Massie 1263 Scratchy Sound
Post by: oogabooga23 on October 24, 2022, 09:31:43 pm: Whenever I turn the volume knob on my guitar, there is a scratchy sound coming out of the amp. This only happens in 1 of the 4 inputs. I haven’t tested any leakage, but I am assuming it could be a bad capacitor?
Title: Re: St George Massie 1263 Scratchy Sound
Post by: shooter on October 25, 2022, 06:26:36 am: I'd look for a bad connection, either at jack, sketchy solder on the jack, or parts connected to the jack
Title: Re: St George Massie 1263 Scratchy Sound
Post by: sluckey on October 25, 2022, 08:16:24 am: schematic...
Title: Re: St George Massie 1263 Scratchy Sound
Post by: shooter on October 25, 2022, 08:35:34 am: ^^ thanks

I'll add C2 to the mix then
Title: Re: St George Massie 1263 Scratchy Sound
Post by: sluckey on October 25, 2022, 08:57:10 am: Would be helpful to know which input.
Title: Re: St George Massie 1263 Scratchy Sound
Post by: oogabooga23 on October 25, 2022, 09:12:17 am: It was on input 2 above the tremolo, should of specified
Title: Re: St George Massie 1263 Scratchy Sound
Post by: oogabooga23 on October 25, 2022, 09:22:42 am: There also seems to be a problem with the tremolo circuit not working at all. I saw somewhere that they fixed the problem by replacing the 6CA4 rectifier tube, but I don't see how that would necessarily help. Changing the tremolo tube with a known good one did not help either.
Title: Re: St George Massie 1263 Scratchy Sound
Post by: sluckey on October 25, 2022, 09:38:31 am: Quote from: oogabooga23 on October 25, 2022, 09:12:17 am
It was on input 2 above the tremolo, should of specified
What does that mean?

Look at the schematic I posted. There are 4 inputs labeled TREMOLO, GUITAR, BASS, and ACC. Which one is scratchy?
Title: Re: St George Massie 1263 Scratchy Sound
Post by: oogabooga23 on October 25, 2022, 10:26:47 am: It's the one labeled GUITAR, sorry about that
Title: Re: St George Massie 1263 Scratchy Sound
Post by: shooter on October 25, 2022, 10:48:11 am: Quote
happens in 1 of the 4 inputs.
:laugh:
took that to mean the 1st of 4, then the schematic inferred Trem as the 1st of 4

I miss the days of reading error logs and diagnostic results :icon_biggrin:
Title: Re: St George Massie 1263 Scratchy Sound
Post by: sluckey on October 25, 2022, 12:10:46 pm: Quote from: shooter on October 25, 2022, 10:48:11 am
I miss the days of reading error logs and diagnostic results :icon_biggrin:
Yeah. We had better communications skills back then and the brain was not cloudy all day! :l2:
Title: Re: St George Massie 1263 Scratchy Sound
Post by: sluckey on October 25, 2022, 12:13:51 pm: Quote from: oogabooga23 on October 25, 2022, 10:26:47 am
It's the one labeled GUITAR, sorry about that
Are you a tech and have a dmm? If so, plug a guitar cable into the guitar input but don't connect the other end to anything. Now measure dc volts between tip and sleeve of the dangling plug. What have you?
Title: Re: St George Massie 1263 Scratchy Sound
Post by: oogabooga23 on October 25, 2022, 07:06:29 pm: I am no tech at all, but I do have a multimeter. I measured 0.9 volts DC in the GUITAR input, 0.5 volts DC in the BASS input, and 0.4 volts DC in the GUITAR/ACC input. For the TREMELO input, I kept getting a reading of 0 volts.
Title: Re: St George Massie 1263 Scratchy Sound
Post by: oogabooga23 on October 26, 2022, 12:39:24 pm: It seems that the problem resolved itself after I removed the death capacitor when I was making a negative feedback switch. I don't know why I didn't remove it to begin with, even though I installed a 3-prong, and the ground switch was useless. With that resolved, I can start to figure out how to get the tremolo working, as the tube lights up but it does not make any sound.