Bought one of these online, foolishly imagining that it would not be too different to a 621 so I would be able to convert into a guitar amp for a friend. After searching around a bit I discover that it's nothing like a 621 
.
For a start it's intended for the UK market, so (contrary to what the seller thought) I don't need a step-down transformer to use it in the EU (Belgium). That's the good news ... however
It could be that the PT and/or rectifier was built into the body of the projector and that I need to add a 240V DC power supply. Then again it could be that this model used the very special power supply that B&H apparently came up with for the 640 model, which takes whatever it gets and uses it to power an HF oscillator
Anybody know anything about this beast?
.For a start it's intended for the UK market, so (contrary to what the seller thought) I don't need a step-down transformer to use it in the EU (Belgium). That's the good news ... however
- I found some images of the whole projector, and it has a weird 5-pin connector ("Jones"?) which is labelled "200-250V AC or DC 6 Amps".
- the amp itself has no visible power transformer (whereas the PT of the 621 is highly visible).
- the valve line-up is completely different to the 621, consisting mainly of PL82s.
It could be that the PT and/or rectifier was built into the body of the projector and that I need to add a 240V DC power supply. Then again it could be that this model used the very special power supply that B&H apparently came up with for the 640 model, which takes whatever it gets and uses it to power an HF oscillator
Anybody know anything about this beast?
I know nothing about that beast but I do know they built many small cheap amps in that era which did not have an ac transformer (they are dangerous and therefore not often ‘repurposed’)..this thread talks about them
Safe Transformerless Amps Possible?
Safe Transformerless Amps Possible?
If this is found to not comply with RULE #3 (note 2) this thread will be locked. Sorry.
I would like to help the OP at least determine what power transformer he can get to use the output transformer. What is the tube complement? With that and the datasheet a power transformer can be specked out. Would be a shame not using the output transformer. If the thread does get locked, take the output transformer and put a low voltage AC on the secondary and measure the voltages on the primary. Then ask for help using the OT.
Also if you could get some interior shots of the amplifier that might help.
Also if you could get some interior shots of the amplifier that might help.
@Printer2 thanks, I am quite willing to do the necessary to make this thing safe, even if it means building a new power supply.
I don't have the thing in my hands yet, but the valve complement seems to be
6 x PL82
1 x ECC81
1 x EF83
1 x weird thing which I am pretty sure is for the soundtrack reader and will be removed anyhow.
When I have it (in about a week's time) I will take some interior photographs - but I expect it to contain some pretty dense point2point wiring.
I don't have the thing in my hands yet, but the valve complement seems to be
6 x PL82
1 x ECC81
1 x EF83
1 x weird thing which I am pretty sure is for the soundtrack reader and will be removed anyhow.
When I have it (in about a week's time) I will take some interior photographs - but I expect it to contain some pretty dense point2point wiring.
The main thing I am concerned with is the power tubes, whether they all are in parallel feeding the output transformer (or the output transformer feeding them). It looked like they all should, I didn't know what all the tubes were. The cathode bias resistor would be what is of interest though. I doubt they would stray too much from the datasheet and you could determine the current rating needed for the power supply. With a pair of tubes in Class A the datasheet says they will make roughly 10-12W into 4k. For three pair that would be a 1.3k transformer, although they might have picked another value. Will make for an interesting amp. Any idea what kind of amp you want to build?
There was a B&H with a small RF-isolated supply for the preamp, and an interstage and output transformer around the power stage. So no large power transformer and nominally safe when sold.
I've seen a picture and I would not work on it. Far too easy to be confused and make a hot-chassis amp.
Yes, the output transformer could be repurposed but that's a small part of an overall amplifier.
I had one like this that I picked up very cheap,though had ul84’s .
Very hard to work in a lot of the old B&H with or with out a power transformer.
I suspect the OT is common across all of the models with 9pin output valve. So Likely you could use that OT for Marshall 18w (or 12 watt for 6bm8).
Very hard to work in a lot of the old B&H with or with out a power transformer.
I suspect the OT is common across all of the models with 9pin output valve. So Likely you could use that OT for Marshall 18w (or 12 watt for 6bm8).
My kingdom for a schematic ...
PRR I've read that the B&H 640 used RF isolation: "In this machine a pair of UL84 pentodes form a power oscillator which runs directly off of the rectified 110V, and via a high frequency transformer supply the power to run the rest of the amplifier – a forerunner of today’s switch mode PSUs". The 640 could work with a magnetic soundtrack, so the RF was needed anyway - that's not the case for the 626 so I doubt that such an arrangement would make sense.
No visible power transformer, no sign of a rectifier for that matter, and the projector could be powered AC or DC (probably using different cables). I'm wondering if I can't just use an external PSU.
Or of course I just gut it and build something using the chassis, OPT and maybe the glassware. Seems a shame though.
Just to be clear - it absolutely has to be safe. Safe enough for a good friend to plug his electric guitar into it - I'd hate to lose him that way.
PRR I've read that the B&H 640 used RF isolation: "In this machine a pair of UL84 pentodes form a power oscillator which runs directly off of the rectified 110V, and via a high frequency transformer supply the power to run the rest of the amplifier – a forerunner of today’s switch mode PSUs". The 640 could work with a magnetic soundtrack, so the RF was needed anyway - that's not the case for the 626 so I doubt that such an arrangement would make sense.
No visible power transformer, no sign of a rectifier for that matter, and the projector could be powered AC or DC (probably using different cables). I'm wondering if I can't just use an external PSU.
Or of course I just gut it and build something using the chassis, OPT and maybe the glassware. Seems a shame though.
Just to be clear - it absolutely has to be safe. Safe enough for a good friend to plug his electric guitar into it - I'd hate to lose him that way.
P.S. This is the continuation of the quote I pasted above (found on PicClick and obviously copied from somewhere else without attribution).
This solution is brilliant and achieves several desired features all at once:
A high frequency source is available to run the exciter lamp to eliminate mains hum, it can also supply the erase head and record bias. The pre-amp valve heaters are also run at HF to eliminate mains hum. No conventional mains transformer is required eliminating weight and a potential hum source. Although some parts of the amp are connected direct to the rectified 110V supply the inputs and outputs remain isolated giving the safety of a conventional AC design. A further pair of UL84’s in push-pull give the amplifier an output power of approx 15W.
This solution is brilliant and achieves several desired features all at once:
A high frequency source is available to run the exciter lamp to eliminate mains hum, it can also supply the erase head and record bias. The pre-amp valve heaters are also run at HF to eliminate mains hum. No conventional mains transformer is required eliminating weight and a potential hum source. Although some parts of the amp are connected direct to the rectified 110V supply the inputs and outputs remain isolated giving the safety of a conventional AC design. A further pair of UL84’s in push-pull give the amplifier an output power of approx 15W.
Printer2 agree with you about the 400V Fender Deluxe clone
It's just possible that the rightmost pair of PL82s is for the PS - they are close to the Jones socket and the perforations in the chassis could be telling us something about what is inside.
On the other hand ... I'm looking at the pictures of the whole projector at 403 Forbidden . On Pic 6 you can see a voltage selector and the label that says "AC or DC". Could it be that the "real" power supply is behind the grille on the upper left?
It's just possible that the rightmost pair of PL82s is for the PS - they are close to the Jones socket and the perforations in the chassis could be telling us something about what is inside.
On the other hand ... I'm looking at the pictures of the whole projector at 403 Forbidden . On Pic 6 you can see a voltage selector and the label that says "AC or DC". Could it be that the "real" power supply is behind the grille on the upper left?
One on Youtube working as guitar amp
This is intersting. Should be similar no PT model.
Bell & Howell Rare Great Britain Filmosound Model 631 Amp with RSD UL84 and ECC83 Tubes 1950's - YouTube
This is intersting. Should be similar no PT model.
Bell & Howell Rare Great Britain Filmosound Model 631 Amp with RSD UL84 and ECC83 Tubes 1950's - YouTube
Hello Gnobuddy. Yes, I know I will need and isolation transformer. Two of the four PL82s are for the video part of the projector. So they will go. And I will probably get rid of the PY82s for solid state diodes. Removing those will get rid of a lot of current draw. I think 500 to 750VA should do it. I will be converting in to a guitar amp. It's just a matter of picking up a transformer for the right money to make it a worth while project. Thanks for your message. Stay safe.
> 500 to 750VA should do it.
A classroom or whorehouse(*) 16mm projector, without motor or LAMP running, can't possibly be over 120VA.
(* Pattern for Panic, Richard S Prather, 1954)
A classroom or whorehouse(*) 16mm projector, without motor or LAMP running, can't possibly be over 120VA.
(* Pattern for Panic, Richard S Prather, 1954)