Standel Amplifier

[devilsindetails]

A friend brought in this interesting amp the other day.

Made in the U.S. by Standel circa 1960s.

There's no model number on the amp but some research I've managed to conduct indicates it's a piggyback Artist 50?

Found very little info on this amp anywhere including at the Standel Amp website.

The PT and OT test ok but it needs a complete cap overhaul...still measuring resistors too.

My question however is although the tube complement is marked 2 X 6DQ6 and 2 X 12AX7 the 6DQ6 sockets are 9-pin...not octals..so it's obvious someone swapped out the sockets for something else.

Was there a 9 pin equivalent to the 6DQ6? I haven't found one in any of the tube cross-references..so I am guessing this amp may have been converted to accept 6BQ5s? Whata you guys think?

As the amp came without tubes I am in the dark.

I am including some pics of the chassis.

Anyone have a schematic for this? Advice? Insights?

Thanks in advance...Leo

[billyz]

I just had a similar Standel in for repairs. But it had a 5u4 rectifier and a pair of 6l6's. Chassis looked identical to yours.
I was never able to find a schematic but it looked very much like the 25l15.
They seem to have used different power tubes at various times.

[Phil_S]

Very interesting. Using Duncan's TDSL parametric search feature, I came up with a list of noval tubes that are a reasonable equivalent, using 20% tolerance on heaters=6.3V, Ra =20K, S=6, and Mu=120 -- the parameters listed for 6DQ6. Based on what I'm seeing, I suspect best bets are 6BQ5 (EL84), and 6GK6 (a great 6BQ5 sub with different pinout.) Lots of others to choose from, though. Good luck with it.

[devilsindetails]

Thanks fellows...I was afraid of that....will have to reverse engineer this but I too am guessing the 6dq6s were swapped out in favour of the EL84s.

[Phil_S]

Thanks fellows...I was afraid of that....will have to reverse engineer this but I too am guessing the 6dq6s were swapped out in favour of the EL84s.

This doesn't strike me as anything to be concerned about. If the wiring matches EL84, just go with the flow. If you don't care for how EL84's sound in this amp, that's another thing all together!

[devilsindetails]

Thanks fellows...I was afraid of that....will have to reverse engineer this but I too am guessing the 6dq6s were swapped out in favour of the EL84s.

This doesn't strike me as anything to be concerned about. If the wiring matches EL84, just go with the flow. If you don't care for how EL84's sound in this amp, that's another thing all together!

Hi Phil...no I meant the fact there are no schematics for these Standels...rectification seems to consist of a couple of old diodes and two filter caps...would have been nice to see how this was originally implemented as my amp has been fudged up quite a bit previously.

[ISOTone]

looking at the 3rd pic, albeit out of focus, it looks like the 6DQ6 were subbed with EL84/6BQ5.

blu and brn - plates - blue pin 7 outer tube, brn pin 7 inner tube
wht/red wire - screens strapped pin 9 to pin 9
wht/grn wires cathodes - strapped pin 3 to pin 3
yel wires - control grids - one phase to pin 2 outer tube; second phase to inner tube pin 2
wht/blu & wht - filaments - strapped pin 4 to pin 4 and pin 5 to pin 5

[devilsindetails]

Thanks ISOTone!

[ISOTone]

Thanks ISOTone!

you're welcome.

[oldmacman]

Sorry to bump a thread from a long time ago, but this appears to be the same circuit as a Standel 20J12. The power tubes are 6BQ5 in cathode bias. This wasn't converted; the 6DQ6 tubes are what the larger S-80 (~30 watts) uses, and it appears they used the same chassis to build the S-50 as well.

I'm working on a schematic based on several sets of photos and will post it when it's ready.

[Phazor]

Looks like the Voltage doubler power supply. I have a 6bq5 standel amp but newer than this one and used the PNP Black SS modules. All modules are missing. The caps in mine look exactly like this one with the big black diodes in a voltage doubler with those Orange Caps. It put out 360 volts DC. When I changed the caps to a pair of 100uf, The voltage went up to 400volts which is a bit much but they run the screen voltage down around 150v so it throttles down the current draw through the tubes. Mine puts out a solid 20 watts with a pair of 6bq5s. I'm going to put an extra 12ax7 for a cascade preamp to feed the power amp but have not got around to it. I'm interested in the schematic you draw up for yours. I have not found a lot of early standel all tube schematics.

[oldmacman]

My schematic is at https://ampgarage.com/forum/viewtopic.php?f=6&t=31949.

I'm curious what the phase inverter looks like in yours. Let me know if it's the same as in the schematic I posted. Also, are there any markings on your PT/OT? Any gut shots you could post would be much appreciated.

Thanks!

[Stevem]

The gray belled transformer looks like a Triad brand.