Hello, I’m new and abandoned Marshall for Fryette 2/90/2 and Bogner XTC.
I bought today in Geneva, second-hand, a Fryette 2/90/2 from April 2010. Channel B works well and no background noise. Channel A also works but with a growl around 50hz. What do you think this could come from? I’m thinking of all the capacitors that are 15 years old that should be changed? (I am equipped and capable of working on tube amps) A technician equipped with a lamp meter also offered to diagnose the tubes, in exchange for a bottle of Jack. Thank you for your suggestion.
VIDEO/SOUND : https://drive.google.com/drive/folders/1PdCIDD4OW2d0DeOzDvw-TMp92N6ghc1F?usp=sharing
Patrick La Cadiere from Azur in French.
Welcome to the forum Patrick.
Thanks for the photos. Everything looks pretty good in there.
It is very unlikely that the capacitors are the problem.
Check the 12AX7 and 12AU7 in Channel A.
Sometimes they can develop a hum if one of them is leaky.
I would swap each of those with the ones in the B channel, one at a time.
Dave
Thanks David,
I’ve already done this, no more noise for 5 minutes then the noise gradually returns.
Yesterday I ordered a complete set of 4+4 tubes and the 13 capacitors, upon receipt I will start with the small tubes then the kt88, to be continued?.. for the capacitors, I wonder if after 15 years they still have good values what do you think? I can measure them or even exchange them if necessary? Before dismantling the card, I prick myself or with my discharger or ? I don’t have a diagram and I don’t want to end up with a curly head like Robert Plant or Louis XIV Thank you David Good Day !
There is absolutely no need to change the caps, so I would not waste the time and money on that exercise. You will be disappointed when it doesn’t affect the outcome.
What brand and exact type of 12AX7s are in there now?
This is a key piece of info:
I’ve already done this, no more noise for 5 minutes then the noise gradually returns.
Here is something directly related to that clue that you might try since you seem technically inclined:
There is a small tan colored disc capacitor on the top middle area of the power tube board below the two 100 ohm filament balance resistors. Take that out and replace it with a piece of 18 or 20 ga solid buss wire.
Let me know what happens.
Dave
Hello, David,
Thank you for your help !
I finally received four new tubes: two PSVANE 12AU7s and two TAD 7025-Ss.
After replacing the four tubes, the amp works very well. There’s no more noise at startup, during operation after 20 minutes, and at shutdown.
I also received four new Psvane KT88-PT tubes to replace the SOVTEK tubes (set the bias to 50mA > 72mA), which don’t have a good reputation on this forum. I’ll replace them later, using the procedure on this forum: Is 72mA on the fuse holder correct for this KT88PT tube model? (See PDF) I’m also going to test the 100W power with 1Khz 500mV on the IN, a 200W/8Ohm resistor on the OUT speaker, and a Scope for peak saturation. Is this correct for this 2/90/2?
I’m very happy 
:
1/ The sound of this amp is magnificent, and the Presence and Deft potentiometers are effective!
2/ The 60/100 power selectors and 2 tube speeds allow for studio use in good conditions.
Our next Hard-Rock concert is on May 15th. I’ll post videos on this forum on my YouTube channel. Rock’On 
KT88-PSVANE-datasheet.pdf (407,2 Ko)
Thanks for the feedback.
I’m happy to hear you’re making progress.
Re: the bias. Use the 72mA spec. 50mA is too low.
Let me know how the Psvane KT88s work out. They’re great sounding power tubes. We’ve had a run of 6550 that is causing a bit if grief recently but they’ve been very cooperative in getting issues resolved.
Dave
