Tube Amp Archive

Hi Yes those 2 resistors were replaced early on, the 5.6K was nearer 7K and the 10K was starting to burn up. Ive replaced the filter cap in the bias circuit and replaced the 2 x 470R screen resistors tonight. All seemed quiet but it tricked me last time i thought it had cleared up. l'll leave it on ...

Ive run it up with out any of the front end valves in place so just the phase splitter and EL84's, crackle are pops are still there. Its almost like you have to replace any resistors and caps that have HT anywhere near them. So something in the power supply, graphic eq or output stage i guess. I tak...

Thanks l'll give it go.
Do you think the EQ is working correctly so only the graphic is enabled when switched to the high gain channel?
Still got pops and crackles to sort out as well...

Thanks for clearing that up, so its basically creating a potential divider if i get the correct idea of it?

Hi Guys Thanks the input, i appreciate your interest. This amp has become my Sat morning mission, its starting to drag on a bit now... Anyway i've replaced the 3 x 30uf 450V caps today, its seems to helped the erratic 50hz (UK!) hum that would suddenly cut in then drop out again. Having tested them ...

Ive picked up 3 new 33uf 450V caps from RS, pretty reasonable cost. Do you know a good place to look for ideas for bias mods to make it variable? I was going to have a look at a few Marshall designs to remember how they do it, its been a long time since ive worked on one of those. Ive got an idea on...

Hi Thanks for that, what you say seems more like what i was expecting to see so its definitely a bit higher than it should be. I am aware of the fixed bias situation with it, i guess i could modify it to allow adjustment but we were trying to get back to factory condition as its already been got at....

Anyone know what i should be measuring as per factory spec?
I measure approx 32mA @ 395 plate voltage with one set of tubes in there.
Cutting max plate dissipation a bit close i think at around 12.6W.
Nothings glowing though at that even when up to clipping.

Yes exactly that, seemed very sensitive around V2 area to the point that i changed the socket after trying to clean and re-tension the contacts. I was starting to think a component issue, i tried a few around that area but it still played up. Ive also fitted a another set of tubes, same problem. Rem...

Hi Not checked the supply caps yet as i still need to flip the board over, i was trying to do as much fault finding as possible with it all in place. Found few high value dropper resistors and new replacements are on the way. l'll do the screen resistors while im there. Have cleaned the pots with Cr...

Hi thanks for the reply. Found a number of dry joints forming around the valve sockets and other areas, re-flowed those but problem is still there. l'll try cleaning the output and phase splitter sockets a, ive only done the input stages and reverb drive. I need to replace a number of resistors to g...

Hi all First post around these parts. Got a Studio .22 in for repair which as a number of issues. Its been got at in the past so some less than ideal looking work has been done. Its had the usual graphic EQ dropping out issues with the O/C 1k resistor in the foot switch supply, this one has been mod...