66 Bassman - The Laurel & Hardy Mods -

[David Root]

"This is another fine mess you've got me in, Stanley"

Customer says this amp had some mods done (four extra holes in the back apron) which were "put back to stock-I was told". He thinks the choke was damaged and gave me a new one to put in.

I'm just beginning to go thru it-- besides the obvious, the power supply has been messed with too. I don't think I've ever seen one this bad.

Anyone seen this before? Note the handwritten tags on the back apron near the extra holes.

[tictac]

Looks like a easy fix though....

Sadly that mod-job looks professional compared to a Torres hack-job

Are those polypro orange drops? Got plenty of lead length on those puppies...

TT

[David Root]

Those orange drops are 600V 715P and Mallory PVC. The two on the right are both .1 uF, should be .01 ceramic. The Bass channel seems to be relatively unmolested, it gets worse as I move to the left.
Yes they are all floating on full length leads, like they were tacked in to see if they would stay in or not. The red leads on the right are coax, replacing the original hookup wire. Will leave those be for now.

It does seem to have been done by someone that knew what they were up to though, as you say, leaving aside the floating ODs.

The good news is the choke measures OK, 94 ohms and 3.4H.

[martin manning]

Installing the orange caps with full-length leads is just weird. Maybe they were just being auditioned? TT is right though, it could be much worse!

[David Root]

Upon further examination, it's not quite as bad as it looks. Some other caps need changing, the 120pF bright cap on Normal channel vol pot is 390pF, I have an original 120 from when I took a beat up '67 apart to build my snakeskin 2nd gen ODS.

There is a 500pF cap to the Normal treble pot instead of a 250pF, and no 500pF across the corresponding plate resistor.

I have enough blue molded caps to replace all the orange drops, (except the two on the right which should be .01 ceramics) and enough saved up '67 hookup wire to replace the red coax leads.

The main PS board has had all the original diodes changed to 1N4007 and six sets of 470K and .01uF snubbers added. The bias cap is only 33uF 63V, I will probably up that a bit. I still have an original '67 PS board, wonder if I should use that instead?

I might do a doghouse recap, as I have to fix up that series-ed first stage cap job anyway. Can't really tell how old those Illinois caps are. The orange drops are from '02 and '04 but the first cap on the right is an MIEC which would I think be more recent. I use those myself.

The PI tail is two 10K in series instead of 22K, and there are some other cheap looking CFs that I'll change back to CC. I will also change those radial cathode bias caps to axials, at least they'll look halfway respectable then.

The customer gave me a box of tubes that has at least six RCA blackplate 6L6 in it so I'll have some fun when I get to that part!

[xtian]

What a coincidence. I just finished a 66 Bassman AB165 refurb this morning. Took five hours, which was two longer than I quoted. Replaced the power cord, all the e-caps, redid the PI, all new recto/bias board, screen and grid resistors, reversed some mods. Sounds great. But original Bass channel Bass control does nothing, even though wired correctly.

[David Root]

How about that! I'll watch out for that Bass channel bass pot.

Just talked with the customer and he wants the full monty restoration as much as possible. I'm going to enjoy this one!

[xtian]

Does he want AA864 spec? Here are two nice articles on the differences and mods:

http://acruhl.freeshell.org/mga/main/AA ... AB165.html

http://www.tone-lizard.com/Bassman_Modifications.htm

[David Root]

Thanx. I don't think so but I'll check. He may not have thought of it, and I have to admit I didn't either. They are definitely different!

[rp]

Here's some TAG info:

http://ampgarage.com/forum/viewtopic.ph ... od+choices

[David Root]

Decided to start with the Tone Lounge mods, to stay close to AA864. Customer may not want to do Billy Z's Longhorn mod, although I find it most interesting, because it involves changing pots and going a bit off the AA864 reservation.
In addition I think it might be not be quite warm enough for my customer overall, he is on the warmer end of the preference spectrum. Could be wrong on that, could depend on how hard you push it, it looks like a balls-out gigging level mod.

[xtian]

David, don't mean to hijack, but hope you enjoy the photos.

Owner just picked up his '66 Bassman. Man, it performed great. Super quiet at idle. Normal channel is perfect clean fender. And jumpered channels kicked BALLS with an SG into a 2x10 cab. Owner left with a huge grin, and I think I sold the 2x10 cab as well!

As you can see, I beefed up the filtering: 80+80, 47 (was 22), 22, 22, 22 (was 16). Kept that last filter stage in, as in the AB165. Totally rebuilt the NFB and PI to AA864 spec.

Good luck!

[David Root]

Thanx xtian, I was wondering how to add in that 100 ohm in the PI! Nice work on the layout!

What are the two non-blue molded caps? I know what the yellow one is.

[xtian]

Mystery cap is an Astron. An earlier mod.

[pdf64]

Nice work!
Lovely clean boards with new resistors and ecaps.
Had one of the 220k feedback resistors burned up?
I'm not keen about screen grid resistors being uprated unless a B+ fuse is added, but I may be on my own on that point.