Tube Amp Archive

M Fowler wrote:It looks like there is a ground wire on the jacks going off to the left side check to see if that is going to the chassis grounding. The other wire goes to the imp. switch.

Mark

I'll check it. Thanks.

Hazy

UR12 wrote: I wasn't refering to the input Jacks I was talking about the jacks where the speakers plug in on the back of the amp.

I never touched the speaker jacks. I did replace the input jacks. Could the speaker jacks have come un-grounded?

I was off-line for a few days without a modem.

Thanks,

Hazy

Like Structo aluded too, make sure those cliff jacks used for the speaker jacks are grounded. Because of the negative feedback coming from the secondary of the OT, if the speaker jacks aren't grounded or loose their ground you will get hum. I'm going to check the input jacks' ground again. I replac...

I really like G&L 3-pickup ASATs: [IMG:778:614]http://i123.photobucket.com/albums/o285/hazy_2007/ASAT_SGroup1-1-1.jpg[/img] I also like old Fender and Marshall heads made into 1x12 combos: [IMG:700:493]http://i123.photobucket.com/albums/o285/hazy_2007/Front1-1.jpg[/img] [IMG:700:571]http://i123.phot...

Have a qualified tech check out the filter section to see if any of the caps have gone bad. I replaced all of the filter caps - twice - with F&T 50/50 uf caps. I checked the ones I put in 2 months ago after I replaced them last week and they were fine. I pulled the caps to and from V2 and checked t...

Jana: It's hard to tell from the pic, but, the green wires are up off of the amp chassis. I did that the other day putting them as high in the air as possible - no noticeable change in the hum. The input jacks are plastic with metal nuts on the outside of the chassis. They used to have the plastic b...

Thanks, solderstain. I've pulled V1 and the hum is still there. I've replaced nearly everything that touches V2 - since I think that's the spot - but with no luck. Yesterday, I added the 100ohm pot and it made no difference (so I removed it). BTW, the 4 input jacks are metal as I changed them years ...

I already tested all of the input jacks and they are not the source of the hum. I forgot to mention that in the original "what I've already done" section. I had to replace V5 power tube socket a couple of years ago...forgot why, but it was bad. Is it possible that the center tap in no longer the bal...

Find the existing centre tap on the transformer (heater supply) and disconnect it from ground. If it doesn't have one, then look for a pair of resistors soldered from each heater wire to ground and disconnect those instead. Basically you want to whole heater supply to be unconnected from anything e...

Last question: How do I install the pot on a Marshall 50w 1978 Drake PT? I can do the work; I'm just not sure where to make the connections. I'm not a newbie to working on high voltage amps...I just can't get this fixed. So, if you are familiar with a Marshall PT from 1978 (50 watt) and where I need...

I'm working on a 1974 Marshall 50 watt super lead that has, at some point in its life, been modded to run 6550s. A couple of months ago I recapped the amp, it it was working fine. I have a similar problem - not yet resolved (thread on this page). Re-capped a 1978 50w MKII. A month or so later - dee...

Dude, it's a 100 ohm trim pot! It would be quicker to try the thing out than to wait for "maybe" answers on some internet forum. Also, you can use any value from 100 ohms to 1k. (I prefer to use 500 ohms since some trim pots are only rated for 200mW or so). Make sure you disconnect the existing hea...

1st off - I'm a newbie to the forum and just found you guys with a Google of my problem. My Marsall 50 JMP (4-hole, 1987 schematic model) has a 60-cycle hum that won't die. I figure 60-cycle because I downloaded an audio of 60-cycle and that's it. I read the thread here where the final solution was ...