Fender 59 Bassman Burnt Resistors...Can Anyone Help with Issue?

ivan H said:
Ok, I've been looking at a few pics of 59 reissues online trying to find this exact board (unsuccessfully so far), but what I have noticed is that the power tube "screen grid resistors" are mounted on the board in this area, so I'm thinking the two burnt resistors are these screen grid resistors. These are fitted to prevent the screen grids from over-dissipating & take the brunt in the event of this type of power tube failure. They would be 470 ohm, 1 watt resistors & of the "metal oxide" type like it appears these are. It appears kinda like one has burnt up & cooked the other beside it & this also makes sense.
Now if these are the screen resistors, a repair would entail replacing the two 470 ohm/1 watt resistors. Possibly replacing the screen supply filter cap (but maybe not). Replacing & biasing power tubes. Hope this helps. Cheers
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Thanks Ivan H! This is exactly the type of info I was looking for! The guy has agreed to $400 and I'm buying it!
 
syscokid said:
Could a bad power tube have taken out that screen resistor?
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It is usually just a matter of playing to much with power stage distortion. If Your'e lucky, everything else has survived. But now You know how the first buyer has mistreated the amp.

If You want to avoid that in the future You might increase the value to some 680Ohm to 1k. 1W because of the larger voltage drop over the resistor.
NOT 2W - a screen grid resistor could act like a "fuse". And, of course with more space for the air flow.

If You want to reuse the PCB please do remove the black stuff (which is mostly carbon, i.e. conducting) as careful as possible. With a sharp knife. Even a hole in the board is less of a problem than a conductin spot.

Well and rethink if that amp is really worth buying. Or translate Your knowledge into a further reduction of the price tag.
 
I have a Pace Soldering station at work that does amazing work on PCB's. If it was just a guy using to much power stage distortion it should be an easy fix. I have the resistors on hand.

If I have to I'll take it to my amp guy and have it completely gone over.
 
bea said:
NOT 2W - a screen grid resistor could act like a "fuse". And, of course with more space for the air flow.
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This is a good point (as is removing the carbon from the board, as carbon is conductive). If in fact they have used 1/2 watt resistors, this may well have been a contributing factor in the resistor frying. You really what 1 watt resistors. 470 ohm 1 watt screen grid resistors will be fine with 6L6's, even in heavy overdrive conditions. If you check old tube application manuals you'll see this value recommended for 6L6's in this class of operation (Leo's early amp designs were pretty well lifted straight from the RCA tube application manuals).
Some people do fit higher value resistors to further limit screen current, however it will change the way the power amp responds, making it more compressed. Cheers
 
If it's too costly to repair the existing board, may I suggest one of these.

www.mojotone.com

Tweed Bassman 5F6-A Style Small Parts Kit

This 5F6-A small parts kit includes all resistors, capacitors, pots, switches, knobs, jacks, sockets, wire and screws (see picture). Tweed small part kits also include the main fiberboard(s). Unfortunately we can't offer any substitutions in this particular kit. DISCLAIMER: Some of the parts...
www.mojotone.com www.mojotone.com

here's the layout

 
This thread is reviving some old GAS of mine: Converting my old Carvin Vintage 16's pcb to a point to point turret board. I already have done a similar conversion to my '81/'82 JCM800, which was pretty easy because proper parts were easily available and the pots, jacks, & tube sockets were already chassis mounted. On my Carvin, these same components are all mounted to the board, which means that I'll have to really think this out... and that's going to hurt all that mush between my ears... :run:
 
syscokid said:
This thread is reviving some old GAS of mine: Converting my old Carvin Vintage 16's pcb to a point to point turret board. I already have done a similar conversion to my '81/'82 JCM800, which was pretty easy because proper parts were easily available and the pots, jacks, & tube sockets were already chassis mounted. On my Carvin, these same components are all mounted to the board, which means that I'll have to really think this out... and that's going to hurt all that mush between my ears... :run:
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You really do not want to mess with that Vintage 16, I suggest you just send it to me.
 
67plexi said:
I had a Fender Blues Deluxe do the same thing it's from a shorted out 6L6GC tube

If it was me I would build a new board and replace the pot's and tube sockets test the speakers make a real amp out of it.

This is a Bandmaster I turned into a tweed bassman

View attachment 28743
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I have that speaker but in 15" in a Deluxe Reverb cabinet. I had to use a eber Beam Breaker with it to cut the periceing treble form the speaker.
 
67plexi said:
I had a Fender Blues Deluxe do the same thing it's from a shorted out 6L6GC tube

If it was me I would build a new board and replace the pot's and tube sockets test the speakers make a real amp out of it.

This is a Bandmaster I turned into a tweed bassman

View attachment 28743
Click to expand...

I may build a point to point turret board for it. I'm going to start with the easy route and repair the existing board to see if it shakes out...
 
Sp8ctre said:
My daughter picked up the Bassman yesterday. Unfortunately I won't see it until Saturday...
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You are a brave soul.... I just won't buy used gear. Too many problems with it in the past to be able to earn money with it, but I am interested to see how this job pans out...
 
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