68 Silverface Bassman rebuild

[TWANG]

http://imgur.com/Dlz3eSO

played for over an hour, still needing tweaks and clean up but..
sounds pretty darn good.

[Firestorm]

I did try a new 12AT7.. brit mullard..
and it tests better than my RCA which is microphonic and his brit mullard
lit up really bright. not red plating but just xmas tree inside.

A lot of European preamp tubes have a little extra filament thing inside that flashes bright when current is first applied. It takes stress off the actual filaments and is exactly what it supposed to do. Looks scary, doesn't it?

[TWANG]

Yeah.. it's not redplating but it's really bright all the time.

I've got a box of AT7s.. so today while I'm swapping tubes and testing
I'll try to do all of them and see which is doing what.

[Baddog01]

I have the bias Rs set for 39.4 and 41.3.. pretty close!
that dropped my plate and screens to 454/453 respectively.
More cleans... I think it sound better.
I couldn't get this close using the GEs.

I have the Russian tubes in.. which are closer to 5881, and I have another set, supposed to be matched that are 6L6GC, so I'll be trying those and I have another pair, too.

I did try a new 12AT7.. brit mullard..
and it tests better than my RCA which is microphonic and his brit mullard
lit up really bright. not red plating but just xmas tree inside.

I will probably try AX and AY 7s' in the AT7 spot.




I like the bass ch. better now than anything so far. but it seems
still .. something lacking.
I think it's time to play it for a couple hours and get to really hear the thing.

Every Mullard does the flash thing but I don't think the where ever brighter than a RCA . Hmm I could be wrong though.

[TWANG]

I found another that lights the same way.
It's nothing since the V's are fine.
got motorboating now.. Norm chan. vol. high.. argh!
hard to chase.

amp sounds really good.. and I've got the mod ideas I want for the bass ch. waiting for this boat to get by.

[Baddog01]

Did you intall new tube sockets? Maybe try reversing the output transformer leads at the plates of the 6l6's. I've seen weird things with the output transformer leads messed up. Hmm

[Baddog01]

I posted " Dumble Mod for Fender Bassman 50" in this forum. Check that put maybe you can get some ideas for you bass channel.

[TWANG]

I found the pop. I think.
the grnd from the cap can.. broke in my hands.
this solid core stuff is crap!
I will replace all the wire from the cap can.
I've already dumped a lot to the tubes.

It has three new sockets.

About all that's not now besides the transformers is the diodes
and the pots.
does have one new pot.


I am hoping the motorboating was a sub symptom of the pop.
I'll test and see once I have the new cap can wires in.

And the OT wires have never changed in this build, but I'm keeping that in mind.

Also I'll look at the dumble thread, thanks!

I don't know what to charge for this. *L*
on the other hand, I really feel privileged having it on the bench.
Boy it's fun even with the swearing.

[TWANG]

New wires to cap can
a few more to the tube sockets..
and a new resistor just for kicks.
*better than I had at the time*

still pops from sby to play.
still motorboats on Norm ch above 8 or so on vol.

back in!


ed did it

pop still there.
but replaced one of the two remainig orig. parts..
the two dual 25uF25V caps.
and the motorboating is gone.
was gonna do this earlier but only had two caps, need four,
so was waiting.

now the dang pop.

[Baddog01]

Double and triple check your grounds. Do you have pics?

[TWANG]

I found the motorboating. see the two 25uF25V caps in the middle..
I replaced the old dual caps.
still have one in.. waiting on parts.

I have found a 200W iron.. garage sale
and redid all the chassis grounds.
in fact point to point on the meter I don't even get an ohm fraction.
I had redone the cap can grnd... and when I went to check it, it fell in half.
solid core wire was shot.
I replaced all the wires to the cap can with stranded copper core silver plated teflon coated wire.
and a lot of the other solid core wires are gone too.

Still no harm looking again.

Here's a pic. ignore some slop.. this is done this way because I am still getting to the 'modding' phase.

[IMG1843]http://i.imgur.com/9nDj0BG.jpg[/img]

[IMG1843]http://i.imgur.com/mc41Irx.jpg[/img]

[Baddog01]

Can you take a pic of the standby switch area and the doghouse?

[Baddog01]

This might help you find your problem..

http://www.geofex.com/

On the left side of the page click on Tube Guitar Amp Tech Page then in tue center of the page click on Tube Amp Debugging Page. When you get to the next page click on Popping Sounds.

This is a good sight to creat a shortcut too.

Hope this helps.

[TWANG]

I have that and went through it all.
plus this
http://www.analogbros.com/tech/articles/goodgobad.html

[Baddog01]

Did you try a different switch?