By weight. Different manufacturers used different transformers, so you could weigh it.
Take pictures and share them.
Take pictures and share them.
Also looking at the pics I see two spots for input tubes and two for output tubes which implies the amp is single ended. You can start there classic single ended tubes would be 300B, 2A3, 45. There are certainly instance of single ended amps using a variety of other tubes EL84 and EL34, KT88. Perhaps someone can better tell by the tube sockets I cannot.
They are push-pull amps using octal tubes as finals and 9-pin miniutures as driver and phase splitter. They appear to be made by a skilled home constructor rather than being commercially produced.
Since we are speculating, I would guess a 12AX7 followed by a 12AU7 with KT88/6550 as outputs. The fact that there are no tubes in them may be indicative of problems. Remove the bottoms and look for any burn marks or bulging capacitors, check all fuses for continuity using a multi tester before bringing the amps up with a variac. Don’t want to let the blue smoke out.
Here’s the link to the pictures:
@firstnot if you don’t have anything useful to say then I ask you leave my thread. No need for rude and useless comments. Thanks.
Well, the amp is executed on a circuit board, rather than point to point. To me, that and the red Wima caps might indicate a small production commercial amp, but the physical aspects, such as the woodwork and that inner chassis scream home brew.
Whatever the answer, the builder had considerable skill, the ground buss being laid out very nicely. The bias scheme appears to be fixed bias rather than cathode bias. I would stick with my original guess, though the finals could be EL34 rather than KT88/6550. Is there any way you might find the tube set for the amp? Otherwise the schematic may have to be reverse engineered.
Maybe other amp builders on the forum can see further into the build than I.
Looks like a kit to me. Maybe a clone. Your Uncle may have assembled it himself. Did he have a background in electronics?
Note the printed circuit board. That helps somewhat date the unit.
Can’t see the back of the unit, no picture. Just a guess an on/off switch and an IEC power inlet? If an IEC that would also help date, time wise, the age of the unit. Also someone may be able to age the unit by the capacitors on the circuit board.
As for the tubes used in the amp? Could somewhat try to use the tube socket pinout to some degree. Somebody with a better background than me in electronics/design may be able to tell from your picture.
I think I see a bias trim pot for the 2 power tubes. Just to the right of the fuse and left of the electrolytic blue color capacitor. A square blue color trim pot.
Closing the loop on this thread. I just returned from True Sound in Campbell. Talked to Nick Gowan who researched the pin sockets. He confirmed it’s a push-pull design that uses common tubes. He has high confidence they are EL34 output and 12AX7/12AU7 inputs. He thinks it’s early to mid 90’s, maybe earlier (he identified a cap as being built in 1985). He recommended powering up slowly (variac). @viridian, your guesses seem to be spot on!! Thank you.
surfersf OP7 posts02-09-2019 3:19pm
@ surfersf OP
By kit I mean the circuit board and the electronic components. It may have started with the board and a bag full of components. Your uncle may have soldered all the electronic components onto the circuit board.
If you do not have access to a variac you might want to try this.
Do you have a multimeter? Do you feel comfortable using it? If yes you could power up the unit/s without any tubes installed and take some measurements.
*** First,..... It is possible the DC voltage could be as high as 350Vdc - 420Vdc.
Because you don’t know how long the amps have not been used you should not just plug them into the wall outlet. What you can do is series an incandescent light bulb in series with the hot 120Vac line. This will work as a current limiter.
If you have an extra 3 wire computer power cord the IEC female connector end should fit the IEC inlet connector on the back of the amps.
You will need to carefully cut the outer jacket length wise about 4" to 6" exposing the hot, neutral, and equipment ground, wires. (Pick a spot where you will install the pigtail socket. Remember the light bulb will get hot to the touch.)
Next cut the HOT wire. Maybe, black, or maybe brown, or some other color.
Don’t cut the neutral wire. It is white or might be blue.
Don’t cut the green equipment ground wire.
Connect the 2 leads of the pigtail socket in series with the, (cut in half), 2 hot wires of the power cord using a couple of wire nuts.
For the light bulb use a 60 or 75 watt incandescent bulb.
If you decide you want to measure for voltages in the amps build the test power cord and then post back.
For the testing you will need to buy a couple of multimeter insulated Hook Clip probe adapters for your meter test lead probes.
These prevent/help from shorting out something when testing for voltages with the meter probes inside a hot chassis.
**** ALSO..... Once the unit is energized, powered on, the electrolytic capacitors in the DC power supply will be charged. Even if the unit is unplugged from the mains wall outlet the caps will remain charged possibly for many hours. If you poke your fingers around inside the unit you could/will receive an electrical shock. You will need to bleed off the DC charge off first.
I’m not a robot.