Tube recomendations for a Bassman

[pbman1953]

A band mate recently wanted  to clean out his basement of gear that he'd never use. So I inherited a Bassman model AB-165. The bass has 2 6L6's and 3 12ax7's and 1 at7.

What are most of you using for this amp. There's a local electronic stores that recently started stocking all the New Sensor brands-

EH, Sovtek, Svetland, Tungsol- which one should I get. Most of the matched pairs are going for $35-40/pr.

Also, what type bias is this amp? I heard that some of them are a balance type or traditional or even I heard that you have to match one to the other.

Any help would be appreciated
Thanks

[Dave]

An amp that says AB-165 on it could be one of about 3900 different variations. Tell us the serial number on the back of the chassis to get a better idea of when the amp was built.

Tube brands are a matter of personal choice really.

Dave

[tubeswell]

JJ6L6GC have a good bandwidth but are getting a bad rap lately for quality inconsistency.

Sovtek 6L6WXT is probably more reliable and cost-effective, but maybe not in the league of great 6L6s

The Svet winged-C is the bees knees

[skyclad]

I really like the Tung-Sol 6L6GC in my Bassman 6G6-B.

[pbman1953]

serial

A45541

[Dave]

Looks like a 68 model. Could be AB-165 with some minor variations. Almost certainly not perfectly true to AB-165. By 68 the CBS people were starting to get their fingers dirty.

Probably a bias balance circuit if memory serves.

Also, I believe there is some wierd positive feedback circuit on that amp.

Some people like to "Blackface" those silverface bassmans. Some like the AA864 circuit others like AA165. Most people don't really like AB 165.

However, I sold a 68 like yours a few weeks ago who thought it was the greatest sounding amp he's ever heard.

Truth be told, I could tell you one thing or another about that amp and its bias circuit and be wrong because it seems like right around that timeframe they were changing their minds more often than they changed their drawers.

Best way to find the truth is crack it open and compare it to the layouts from AA / AB 165.

Dave

Dave

[pbman1953]

The white label inside the cab says AB165. I'd like to mod the bias circuit if possible. I could do it if I was told what to do step by step. In my other amps , Sunn 2000s and Traynor YBA-3A super, I've replaced out old parts and have even installed new filter caps. I'm not an electronic repair guy, more of a electronic hobbist that has done alot of soldering over the years. I used to be in car stereo so i've replace many ic's for better sound quality. I've even added, from this forum's help, a second bias pot to my Sunn 2000s. So I can do it but with a little help

[Dave]

OK, for starters go to schematic heaven and look up AB165 and have a look at the bias setup. Yours probably looks like that.
Look at the layout instead of the schematic if you need to, it may be much easier for you to read.

Then look at the AA165 layout and make your amps bias look like AA165 which is a true adjustable version.

Its really not hard at all, especially looking at the beautiful layouts that Fender used to provide. Its like color my numbers.

Dave

[sluckey]

Look at this...  http://www.el34world.com/charts/bias_conversions.htm

[pbman1953]

I have a small suspision that the bias mod may have beeen done. It seems different from this one-

 www.freeinfosociety.com/electronics/schemview.php?id=861

Mine is not like this one

It's like this-

The left leg of the pot goes to the board with the 100mf cap

The center leg goes to the eyelet in between the the 2- 220k resistors

Pin 1 of each 6L6 goes to a 220k resistor


The right leg of the pot grounds to the pot body  with a 15k resistor

If this is the proper bias cicuit please let me know. I have a Bias Right that I bought from Weber that  can bias 6550's, 6L6 & KT88. All I have to do are
formulas for the tube. I bought the one with the built in volt meter so it's totaly safe.

Thanks

[jcm-jmp]

tung sol pre tubes and Ruby yes Ruby in the power

[pbman1953]

I tried loading up the pictures but they're slighty too big to send

[sluckey]

I have a small suspision that the bias mod may have beeen done.

Yes, it's wired for bias adjust, not bias balance.

[pbman1953]

So I suppose that's this is prefered cicuit that the adjustment will effect both?

[sluckey]

yes

[pbman1953]

ok, thanks to all

Rich