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 Back from the Depths of the Locker and Brought along a 63' Bassman

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Davy Jones 24


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Join date : 2014-10-20

PostSubject: Back from the Depths of the Locker and Brought along a 63' Bassman   Sat Oct 25, 2014 2:27 pm

Hi There Mateys! I be back to the forum. I know I haven't been posting in years, somehow I lost me password and had to re-register with a different username. Been checking the site off and on, and keeping up as best as I can. Congrats to TV on all he's accomplished and for keeping this thing going as we all don't post as much as we used to.

Anyway, reason for this particular post is twofold, one to say hi to everyone that I used to talk to on here and two to get some advice on a 63 6G6-B blonde Bassman that I recently picked up. It's in really good shape for its age and it is, LOUD, about matches my 100W Marshall at 5 at a volume level of 2! All transformer codes are original specs. It does have the Jensen speakers and I may switch them for Celestions but I haven't found the English ones yet, and I am leery of using the newer Chinese ones per TV's advice in one of the other posts. I'm including a couple of pictures of the circuit, as it looks like pretty much the original parts in the amp.

So, couple of questions for my own knowledge, as I have every intention of maintaining/restoring this amp. and playing it myself i.e. I'm not trying to resell it to Captain Teague!).


#1: The brown/red capacitors on the normal channel circuit, are they the original spec. ones that Fender used in the 60's or have they been replaced? The other ones look like the original Astron and Blue caps that would have matched the amp. I do need to clip out the one little cap. going to the Bass Channel (per TV's suggestions) get my Voltmeter out and check the voltages/capacitances across all the circuits yet, haven't done that yet and I'm sure some of these have drifted from original values, but from checking the circuit it looks like the previous owner kept the amp. as a 6G6-B and didn't Blackface it (thankfully).


#2: Preamp tubes are not the preferred Ruby AX7's. Actually 3 12AX7's (USA made) and one ECC83. Not sure of the manufacturer. I ordered some Ruby tubes and plan to change them out. Power amp tubes are large bottle Russian Gold Aero. 6L6WGB/5881's. Are they much different from the NOS 5881 Tungsols? So, next question, do I need to re-bias if I switch out just the a) Preamp tubes, b) the 5881's or c) both? If I do have to re-bias, where is the fixed bias-pot for adjustment on the 63'? I've worked with high-voltage circuits before, so I'm aware of the risks, and although I may take it to a tech., I'd rather do it myself. Any of those amp-bias kits out there make the job any easier or safer?

#3: The amp is great. Should have got one a long time ago. When I first started playing it, I let the tubes warm up for about 5 minutes on standby before I started playing. However, for the first hour or two the signal would cut out intermittently. I switched input jacks (1 to 2) on the normal channel and went over to the Bass channel as well, and I can't seem to isolate it. Changed guitar cables too, thinking that was it, but it didn't have any effect. Only thing I have plugged between the guitar (Fender Gretsch SSU) and the amp is the RE-20 pedal (I know, I know, I'm breaking the rules here with a digital pedal Smile). After a couple of hours it seemed to have stopped or else I didn't notice it anymore. I didn't try it with a different guitar, but that's the next variable I need to iron out when I get a chance to play again. Any idea what's causing this and how to fix it? My thoughts were either cable, the guitar input jack, or the amp input jack, but I figure I'd ask the experts.

I'm trying to post the images but not sure if that's working or not, having some issues with it. Might need some help on that too.

Anyway, no rush on replies, if anyone has any suggestions/answers I'd appreciate it, if not, no big deal. Hope everyone's doing well.

Capt. Jones
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Davy Jones 24


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Join date : 2014-10-20

PostSubject: Re: Back from the Depths of the Locker and Brought along a 63' Bassman   Sat Dec 06, 2014 11:56 am

Alright, so after some poking around inside the amp. here's what else I found.



#1: I checked the circuit diligently and got out my multi-meter and checked resistance and capacitance on all of the resistors and capacitors with the amp off. I hadn't played the amp in a week or two, so all of the capacitors were drained. I didn't check them with a capacitance checker at full voltage, but I'm not sure that I need to do that. Anyway, pretty much all of the filter caps (electrolytics) were out of spec. (surprisingly, one of the caps in the pan was fine, others were all off), but I guess that's to be expected since they were the original Astrons that came with the amp. I ordered some Sprague Atoms to replace them with and will solder those up next. While I was at it, though, I checked the rest of the capacitors and found that most of them could use replacing too. Those brown/red ones look like a previous owner replaced the standard Blue Molded Ajax Caps with those instead, and they aren't even the right spec. in certain cases. Same for an orange drop that's in there which is like 100X the proper capacitance rating if you go off the circuit diagram. I found a few resistors that are out of tolerance as well. I plan to replace those and put in a bias pot as well. If/when replacing the signal caps, do you guys use Orange Drops, Mallory, Solens, Blue Molded reissues (i.e. Soso), or the vintage Blue Moldeds pulled from another working amp.? I'm going to go with the Blue Moldeds for the signal caps and supplement them with Orange Drops and Mallorys where I can't find ones with the right spec. I bought a couple of the small ones from the Fender Vintage parts store.

#2: I did a little more research and came to the conclusion that I need to rebias the amp. once I change out the capacitors and the tubes. I'm going to wait until I get the amp. re-capped before I switch tubes. Right now, checking it with the thermometer, Tube #6 is running at about 260-290 degrees F, and Tube #5 seems about 50-60 degrees cooler on average. This seems to be set more on the colder-side, right? Would this explain why the amp. isn't really breaking up as much as I would expect at lower volumes with the treble and presence dimed (i.e. like the more heavier sounds like Brand New Cadillac, Ghost Radio, Drive Like Lightning Crash Like Thunder, etc.)? Anyway, this did bring up a question that I can't seem to find an answer too. I understand how to apply the fixed-bias method, and that's what I'm going to use when I re-bias the amp. but I would like to know how to perform the output transformer shunt method. I understand how to do it in theory, but where would I connect the leads on the meter inside the chassis (i.e. where are the leads to the terminals on the output transformers inside the amp)?

#3: As for the cutting out issue, I ruled out the cables, guitar, and amplifier channels. I bought some of that contact cleaner and I am going to give that a good spray onto the input jacks and see if that clears it up. Strangely enough, maybe it's just that I'm not giving the amp enough time to warm up on standby. I tried it the last time and gave it closer to 15 minutes and it never cut out on me once. I figure between that, the cleaner, and the capacitor change, it ought to take care of it, but I guess we'll see.

Anything else I'm missing/forgetting here?

Hope all of ye had a good Thanksgiving and have a good holiday season!

Capt. Jones
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PostSubject: Re: Back from the Depths of the Locker and Brought along a 63' Bassman   Mon Aug 31, 2015 5:51 pm

you done gone n left again
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