PREMIER AMPS B-160 and B-220

[retrorod]

Hello, Looking for some info on the repair of a Premier B-220 Bass amp 15" combo. A harp player acquaintance brought over his working B-160 and his non-working,newly purchased B-220. The B-220 was damaged in shipment(magnet sheared loose and took out a homeade EF86 sustitute). At some point a 'creative' repairman fashioned a 9pin to 7pin convertor that held a 6AU6 tube and was inserted in the EF86 socket. This was demolished in the loose magnet incident. Is that even a compatible tube subsitute? I have seen no such substitute for the EF86(6267). I know they cost like $50 vs $5 for the 6AU6. Further, the B220 is fitted with 6V6 power tubes and what appears to be factory SS rectification.
The functioning B-160 has the original EF86, has 7591A power tubes, and a 5U4G rectifier vs the 5Y3 that the chassis is labeled. This amp sounds wonderfull with guitar, although the harp player would like a little more power from it!?! Which output tubes are correct for these amps..6L6 or 7591A ?
Seems like the chassis/circuit are almost identical in these two amps. I am just getting into it, however.
I figure I can borrow the EF86 form the B160 to do further testing.
Can anyone shed some more light on these old Premiers? I have the B-160 schem. but can,t find much more than that. Should I snag an EF86 or are there any other substitute mods that could be persued? Thanks!
I can follow up with more info as I get my hands dirty...Rod

[retrorod]

Hi, I brought this thread over from the Harp Amp section, There seems to be a little more traffic over here. This is the only schematic I have found...http://www.schematicheaven.com/barga...60_bassamp.pdf

The B-160 that I have has tube rectifier and 7591A's
The B-220 has factory SS rectifier and came with 6V6's
Other than that...the chassis and layouts are indentical. Both push 15' Jensens
I got the B-220 running. The problem was that the contact wafer on the rotary on/off switch had broken off and was not allowing B+voltage to be applied. I managed to glue and re-enforce it well enough to get it functioning again. Voltages seem to be proper according to the schematic that I have.
I guess the main thing is determining if They have the proper output tubes.
The owner of the amps(harp player) would like them to be less feedback prone. Any suggestions on that? Seems like I have read somewhere about reversing polarity on the speaker??
Any input is welcome...Rod

[stereomonostereo]

I've never heard of a B-220 using 6V6s. Every one that i've seen has had 7591s. Definitely switch it back to the EF86. A 6AU6 in it's place is puzzling at best. The speaker polarity shouldn't have much to do with feedback.

Does it look like the power tube sockets have been messed with? If it was converted for 6V6s they would have needed to change the pinout.

[pdf64]

I'm not clear how that input jack socket switching arrangement works, not even sure whether that cap is cutting lows or highs?
Don't some crystal harp mics work best with a very high impedance input? In which case the 330k resistor could be raised, even ditched (what's it's function?).
Unless there's much voltage across that 2M2 grid leak resistor (ie >0.2V), it might be simpler just to sub in a regular fender input arrangement.
Those tone controls are unusual - is the schematic drawn correctly?
Generally the less frequency shaping the better for feedback resistance. Does the user need a bass control? If not just change it to being a simple treble cut control, see
http://www.schematicheaven.com/barga...mony_h306a.pdf

[retrorod]

Yes,STEREOMONOSTEREO, The pinout HAS been changed to accomodate the 6V6's. I forgot that the owner told me that and I visually verified it. It was probably done by the same guy that fabricated the 6AU6 adapter. The pinout does not look changed on the EF86 socket. It is running 370V plate on the 6V6's. The rest of the circuit looks indentical to the B160.

PDF64, as near as I can tell, the schematic matches the input and controls section of these amps. So perhaps, some changes there would give positive results? Any more specific changes for this particular circuit?....Rod

[stereomonostereo]

I'd definitely switch it back to the 7591s. I've seen people mod them for 6L6s with some success, but never really heard about 6V6s. My B-220 never has any feedback problems

[retrorod]

Hmmm! Thats interesting. The owner has not heard this amp yet, as it was damaged in transit. He has enlisted me to get it going again. Do you use the 220 for a harp amp? His B160 functions fine and has the 7591's in it. The schematic for the B160 shows 6V6 tubes. Perhaps they came both ways depending on the year of make?...I will keep on...Anymore input from others...Thanks!

[stereomonostereo]

I use it mostly for guitar, but i've used it for harp as well with no problems. Let me know if you need any voltage readings or anything