I picked up this amplifier as part of a lot of items at an estate sale. If anyone can identify the circuit and determine what tubes it requires, that would be helpful. There are no markings or brand labels anywhere on the unit. Thanks in advance.
Attachments
Most likely 6BQ5/EL84 single ended with a 12A*7 driver. Rectifier could be anything from a 5Y3 to 5AR4 to 5V4.
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It's probably a custom build or a kit from tubesandmore (Antique electronics) or another tube supplier.
Judging by pic #1 and #2, looks to be cathode biased by the looks of the wirewound resistors to the ground copper wire. Basically what astouffer said. The addition of the heatsink to the power transformer is curious, it shouldn't need that if it's not being pushed to its limits...
Judging by pic #1 and #2, looks to be cathode biased by the looks of the wirewound resistors to the ground copper wire. Basically what astouffer said. The addition of the heatsink to the power transformer is curious, it shouldn't need that if it's not being pushed to its limits...
The B+ is around 350VDC.
Agree that it's a 6BQ5/EL84 single ended amp. The 5Y3 should do for the rectifier.
Measure the output tube cathode bias (large green) resistors.
If you reverse engineer the driver schematic and resistor values,
the driver tube type probably can be determined.
Agree that it's a 6BQ5/EL84 single ended amp. The 5Y3 should do for the rectifier.
Measure the output tube cathode bias (large green) resistors.
If you reverse engineer the driver schematic and resistor values,
the driver tube type probably can be determined.
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That was my guess on the power tubes, any thoughts on what rectifier would work? I have a 5R4GB on hand, wondering if that would be compatible? I assume the center nine-pin socket would be the driver, with the two outer sockets for the EL84 valves. I have plenty of 12A*7 variants on hand, so almost there. I need to get a matched pair of 6BQ5/EL84, as the last two I had just went out with a sold amp.
Thank you!
The 5R4 should be fine.
You don't really need a matched pair of output tubes, since there is only one per channel
and they are self-biasing, but it wouldn't hurt either.
You don't really need a matched pair of output tubes, since there is only one per channel
and they are self-biasing, but it wouldn't hurt either.
Unless you are running screen drive this is not an el84.....this is a 6p1p output tube sold by various chinese vendors.
6p1p is close to a 6aq5 or 6v6 with no pin compatability
6p1p is close to a 6aq5 or 6v6 with no pin compatability
Sure looks a lot like this: https://www.aliexpress.com/item/32791728940.html
Except the heat sink on top of the power trans. 🙂
jeff
Except the heat sink on top of the power trans. 🙂
jeff
Yeah, the inside sure does look similar, but for the tubes, they say:
- Preamp tube: 1 x Chinese 6n1
- power tube: 2 x 6p14 (EL84)
- Rectifier : 1 x 5z4p
Probably a good idea to check the socket connections to make sure they are wired correctly for EL84's. I've seen pics of the exact same chassis with different tubes.
jeff
jeff
https://hifi-exquis.com/8_jbh
You can buy amp with or without tubes as finished amp or just as DIY sets (you can do wiring better than their factory!)
https://hifi-exquis.com/el84-6p14-tube-amp/441-jbh-6n1-el84-tube-amp.html
You can buy amp with or without tubes as finished amp or just as DIY sets (you can do wiring better than their factory!)
https://hifi-exquis.com/el84-6p14-tube-amp/441-jbh-6n1-el84-tube-amp.html
One of the pictures in post #1 shows that for B+ the power transformer has a 265 V - 0 - 265 V winding. I don't think that when loaded this will give around 350 Vdc. At about 90 mA I would expect it to be around 290 Vdc.