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Where can I find EL90/6AQ5 beam tetrode output tubes?

jt1stcav

jt1stcav

Up and Coming Bottlehead
Does anyone know of an individual or online tube store that carries the EL90/6AQ5 beam tetrode valve, especially matched quads? Doesn't matter what manufacturer or if they're NOS or brand new. For some reason these tubes seem harder to find than the more common EL84/6BQ5 pentodes. And what's on eBay are just a mix 'n' match...I need a matched quad.

Any help would be greatly appreciated.
 
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What's the 6AQ5's for Jim?

The local audio buddie of mine has been pondering a 6AQ5 PP circuit for some time using 6005 Tung-Sol's. They make the standard RCA 6AQ5 look pretty wimpy.
 
I had a SE 6AQ5 and got some black plate 6005s. They are good tubes and I would think the prices should be good since they aren't used as much as 6BQ5s.
I only have pairs, no quads.
 
Mike Stehr said:
What's the 6AQ5's for Jim?
Click to expand...
My bro bought one of those lil' inexpensive ($190) Chinese amps on eBay that Sophia Electric sells as their "Baby" model for $899 without mods!

We don't know the name of the manufacturer of this tiny amp...on top of the steel trannie case is a piece of plastic with "Sonice" printed on it; the carton it came in says "Aria Mini"...maybe they're the manufacturer(?). No manual came with it, not even a detachable power cord!

From what the auction said, the amp is driven by two 5670s and the output tubes are 6BQ5, but from the auction pics and all the reviews and pics on the "Baby" (none were found on the "Sonice"), the output tubes are listed as and look like 6AQ5s instead (the "Baby" is sold with Russian military 6P1Ts). My brother Tom received the tubes in their own well-packed carton, but he's got a quad of Chinese 6BQ5s instead of 6AQ5! Because the seller is from Hong Kong and his English is very poor, even after several e-mails he still hasn't made himself clear to Tom whether the amp he sells on eBay takes 6BQ5 or 6AQ5 output tubes, and Tom's not gonna put in the 6BQ5s and risk damage to the amp if it takes 6AQ5s instead. The top plate where the tube sockets are does say "6AQ5", but nothing's printed for the driver sockets.

This is why he's looking for a good source of 6AQ5s...

Thanks again, everyone.
 
OK, this gets more complicated. 6AQ5 is a 7-pin tube, and of course there's no way you could interchange 7-pin and 9-pin tubes. But the Russian 6P1P is a 9-pin tube like the 6BQ5. It is similar in characteristics to 6AQ5 (and 6V6) but different base and pin connections. So you'll need to get the 6P1P or rewire the sockets to take 6CZ5, 6973 (newly available from EH) or 6CM6 (or change resistors for 6BQ5).

If it's a PCB, you'll need them Russkies. Often seen on eBay, and pretty cheap. If it's point-to-point, 6BQ5 would be my choice, reducing cathode resistor for correct bias.
 
You can pull up the pin out diagrams on the tubes and follow the wires a bit, like to the OPT, etc to determine if the amp is pinned out to a 6BQ5. Tom is right about the 6AQ5, it will not fit in the socket of a 6BQ5.

Best check the pin outs though. I am not familer with the Rusky tube but you sure as hell don't want to have something like the plate voltage hitting the cathode.
 
Wish we had a schematic...

Tom and Thatch...you bring up good points indeed. We now have no idea what output tubes this amp takes...6AQ5, 6BQ5, 6P1T Russkies, or whatever! It's on a PCB, and there are 8 solder connections on each output socket (which form an arc...the two driver sockets are near the middle bottom on the PCB).
 
Judging by the solder blobs around the sockets, I'd say they are 9 pin.....or 8?....does that thing even have a power supply fuse?
 
Starting on the left looking down at the bottom the pin numbers srart at one and go from there. draw a circle and put a U shape where the gap beteween the pins are. That will be the key. Then draw a little circle and put in the number. For instance a 6BQ5 will have 9. Cetain pins should be pretty easy to trace the wiring back enough to determine what the pin is for.http://hereford.ampr.org/cgi-bin/tube?tube=6BQ5

here is the data for a 6BQ5. You should be able to follow the input through the 5670 http://hereford.ampr.org/cgi-bin/tube?tube=5670

It looks like you have the inputs in the back and the leads run to a pot or switch. From there it should be wired to pins 3 and 7 (grids) of the 5670. From pins 4 and 6 you should be able to trace on the PCB a path that leads to the grids of the power tubes. If it is a 6BQ5 you will see the grid is pin #2.

The filament is on a 6BQ5 pins #4 and 5, on a 5670 it is #1 and 9. These should be part of the same circuit.

The B+ should go from the power transformer to at least one of the PS filter caps, then into the OPT. From the OPT there should be a wire going directly to the plate of the power tube which on the 6BQ5 is pin #7.

After that the type of circuit comes into play and here I am guessing. Pin #9 which is the other side of the grid is probably hooked to the second stage of the PS caps. There should be a resister between where the wire goes into the OPT and the next cap to drop the voltage.

Now it looks like the filament supply goes to the second power tube from the left 1st and to pins #4 and 5. Looking at the pin out of the 6BQ5 you see the filament goes to pins # 4 and 5. I see a wire from the OPTs going to pin # 7 on the power tubes which is the plate for a 6BQ5.

I would say we have eliminated the chance of it being a 6AQ8, it is probably a 6BQ5 (at least the pin out seems to) but you need to get the pinout of a 6P1T and compare it to a 6BQ5 because they can be the same but with different voltages.

The Baby is a nice looking amp.
http://www.positive-feedback.com/Issue8/sophia.htm
 
Thatch and Tom, thanks again for your invaluable experience and knowledge...I greatly appreciate it (and so does my bro).
 
Hey JT

I know that a friend of mine have those Tubes you are loocking for.
If you want i ask him for the brand and the price and if you agree on that i send them to you.

Ciao.
 
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