1959 100 watt Marshal RIl acting up

[dumbassbob]

My amp is from 1993 when the first 100w.ri came you I have only ever had to change a power grig resistor..I pulled out the power tubes and all the preamp tubes are reading wrong like -345.mv on both the plates and the grids the 6.3 are fine all the way up,When I use the normal chan it is not as loud as it should be,and when I USE THE Higain all hell breaks the 5000pf cap makes microhonic type noise and crackles when I turn volume knobs,Couls All my preamp tubes be bad? I have 20 and some are not as bad as others when I put them in,but after a miniute or so I get loud buss crackle,Also I checked the 30 yrs old filter caps and only the first 2 are reading near 500 V all the others read around 340V. I cant believe that every 12ax7 would read these weird numbers...I am not real good at poking around in this amp..To easy to get killed.Also it gets a low hum some times that doesn't sound right,any help with plate and grid voltages would help it is a plexi RI 1959 from 1993 thanks DAB

[alexradium]

check out all the voltages on tubes,referred to ground,probably filter caps need replacing and some string supply resistor went south.

[Chuck H]

This^^^^^^^^^^^^

And I think you may have a leaky coupling cap in the preamp.

[dumbassbob]

DAB does it again I took it to Classic Amp Repair in NOHO(north Hollywood) the tech "Mike" looked at it and said buy a new DVM not from Lowes. He said it will cost $65.00 and maybe some new power tubes. and may cut the 50140PF bright cap put something a little lower in.

[Leo_Gnardo]

DAB does it again I took it to Classic Amp Repair in NOHO(north Hollywood) the tech "Mike" looked at it and said buy a new DVM not from Lowes. He said it will cost $65.00 and maybe some new power tubes. and may cut the 50140PF bright cap put something a little lower in.

NOHO, bit of a hike from Dana. But that's where the studios & musicians are. Sounds like good advice.

[nevetslab]

DAB does it again I took it to Classic Amp Repair in NOHO(north Hollywood) the tech "Mike" looked at it and said buy a new DVM not from Lowes. He said it will cost $65.00 and maybe some new power tubes. and may cut the 50140PF bright cap put something a little lower in.

Lowes is where you go to buy DVM's these days? Not that I shop at Fry's, but....at least they sell Fluke products. Pacific Ave @ Hollywood Way, just below the railroad tracks.

[Chuck H]

I think Fluke is a good company to support. That said... Being on a budget the last time I needed a DMM I got a used Fluke 87 on *bay. It may have been refurbed because the plastic screen protection was still in place. In fact it still is, so maybe it was just lightly used and well cared for. I'd never had a Fluke meter before. I won't say it's a game changer over my trusted old B&K that finally went funny after almost twenty years, but it IS better in most regards. Little things like it has some weight and longer leads so I'm not tugging it off the bench (as much ). The display is bigger. It has a fast auto range that almost never gets confused about which range to settle in. The rotary switch is sure, but not snappy stiff. And though I haven't broken a meter yet the Fluke seems very durable overall. My old B&K did have better small capacitance measurement. I miss that. But it didn't have higher capacitance measurement capability that the fluke does, sort of. Anyway... I'm going to hope to always have a Fluke now.

[dumbassbob]

I got a Ideal brand DMM for $35.00 but it did not read the preamp tube voltage right,it did read the 6.3 HV,but went haywire on the others readings That or I did it wrong,but the amp tech was joking at me.