1969 Bandmaster Reverb Amp

[plexi50]

Got a 1969 Bandmaster reverb yesterday for a song. Hummm! All the PS caps were so fat and had spewed out there guts inside the dog house. This in turn shorted out the power tubes as i supposed some one tried to use it after it's death. I put in all new PS caps and Sylvania power tubes along with all 1961 Sylvania 12ax7 preamp tubes.  Flipped the switches and the angels gave approval. (put your boots on) Vibrato and reverb are wonderful. Head case is in excellent condition as is the grille cloth and aluminum trim. I made a few changes removing the power tube grid snubbing caps and resistors. Changed the bias to pre CBS and changed the 47k PI pair to 82k-100k. 47 ohm fixed presence and removed the reverb bright cap. It's now 12:30 AM so i have not been able to wail on it yet but the few low notes i heard make me It is dead silent at idle which is another big plus. I also did a few AB763 circuit additions  to the tonestack and some thing else i already forgot what it was. Of course pics will follow tommorrow. This model has and uses an old NOS Sylvania 5AR4 rectifier tube.  I believe this was a AA768 circuit before making changes to AB763

I was wanting to try some old NOS Sylvania 6V6GT tubes. I have 455 VDC on the plates and dont know if i should try this. Im thinking that is a bit too much for 6V6 tubes. I wouldnt want to kill them in a short period of time. I also dont think from the data i read that a 5Y3 would work but maybe a 5U4GB might be a better choice for lowering the plate VDC should i try the 6V6 tubes. Opinions?

I will check the B+ with a 5U4 in the morning

[Raybob]

That is a great head.  I've had a '69 since '91.  I paid $50 back then but it had a blown PT.  The entire front board was gone too.  Made a new board but never did find that silver trim.  I've done the mods with bias and removing caps, etc. getting it same as a Super Reverb AB763 except for the .022 tone caps and the 47 ohm 'presence' resistor, I left the .047 tone caps of the Bandmaster Reverb.  Real powerful and clean to a great extent.  I dated mine from the pot codes, tube chart was missing.  The board looked to be wired as the AA1069 Bandmaster Reverb.

Raybob

[HotBluePlates]

You may want to consider whether replacing the electrolytic cathode bypass caps is a good choice for you.

Conventional wisdom is that they dry out too, so you should replace them. My experience has been that in some old Fender amps, the bypass caps dried up an measured 1-5uF, which made the bass clearer. I preferred the sound with the lower-value bypass caps (some other folks do as well, even if they don't go all the way to Marshall's 0.68uF value).

[plexi50]

Yes HBP i was looking and thinking about that last night. I have them if i want to change them. I know i probably should anyway just for GP. I wanted to hear what it sounded like first. It sounds spretty darn good. But like an oil job it is likely time to change them anyway. I used some 1 uf & 2.2uf cathode caps on another build and was impressed

This is identical to a super reverb circuit and the voltages are the same as well Raybob

I didnt think to look at the super schematic until you mentioned it / I have to have .047 mid caps in my amps. I think they sound better for the mid frequencies

Im changing the cathode caps now /

[rafe]

Those are really great heads.....great score at any reasonable cost........they fetch good money ......

[plexi50]

Reasonable is an understatement. Heaven sent. I just changed the cathode bypass caps. I know those old brown caps dont have a good rep but for now they will have to do. I am waiting on a parts supply. Are these old blue caps in the last pic better than the brown ones? I wish i had some more of the blue molded caps

Will plug and play in a few / Did GOD create tube amps? He must have. The vintage amps look like ingenious masterpieces

[FYL]

Are these old blue caps in the last pic better than the brown ones?

Better? Not sure. But they are highly sought after.

BTW that's the first BMR I see with a mix of blue and brown caps. This could be a transition model, with some stocks of blues left and used by Fender. Or a modified amp: the large 100K / 1 W as well as other components aren't stock.

[plexi50]

Sorry FYL those blue caps in the bag or on the board now did not come from this amp. I have a ton of them in bags from over the years. I really dont know much about them. The blue molded ones i put on the board last night in place of the original brown caps. Plus i am using a .047 instead of the (2) .022 caps that were on the board. I got rid of the brown turd caps and put some Xicons in i have. Amp sounds better with the Xicon PI coupling caps and cathode cap changes made today / 

[FYL]

those blue caps in the bag or on the board now did not come from this amp.

Oh well, could have been interesting.

I have a ton of them in bags from over the years. I really dont know much about them.

Made by Ajax. Good quality Mylar film caps, most are still fine after 40+ years and don't leak.

[plexi50]

Thats nice to hear on the caps. I quess i need to sort the values out and make another place to hangem

What was bad about the brown caps anyway?

[FYL]

What was bad about the brown caps anyway?

Poor construction, a lot of them have become leaky.

[plexi50]

Never got around to trying a 5U4GB tube to see if i could get the B+ in the 6V6GT working range

This amp sure sounds better than the Bassman 50 watt i had. I love the Bassman but it is just LOUD

This amp is 40 watts (OT) and has some Mojo in the mix

[rafe]

From what I understand a lot of the Bandmaster reverbs end up as Vibroverb clones, they sound kind of close with out modification .........

[FYL]

From what I understand a lot of the Bandmaster reverbs end up as Vibroverb clones, they sound kind of close with out modification .........

Same chassis, not exactly the same circuit, not the same OT : the conversion is very easy.

[Dave]

Yeah, you won't be able to get away with using a 5Y3.
That amp (regardless of what the tube chart says) came stock with a 5U4.
The PT's that had CT's for the filament winding were designed with 5AR4's in mind
But when they dropped the filament CT in favor of 100r artificial CT's they also bolstered the 5 volt winding to handle a little more current draw and accomodate for 5U4's.

Deluxe Reverbs usually run around 420VDC on the plates of the 6V6's. I have heard a lot of people says that that is too much for them, but Deluxe Reverbs work real good don't they?
A 5U4 is not going to get you  down to 420, but it might get you in the general neighborhood.
If you have some expendable 6V6's, you could give them a try. I'd double the speaker load.

Dave
 

[plexi50]

Im going to pass on the 6V6 thought. One interesting point here though is the Bandmaster Reverb schematic shows a 375VAC secondary to the 5AR4

But my transformer has a 360VAC secondary to the 5AR4 as shown on the Super reverb and Vibroverb schematics -5VAC Vibroverb