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Thought someone might enjoy these shots of the VHT Valvulator. I've got it apart right now replacing the poorly designed power transformer. The tranny solders to the PCB which rests on it's side in the housing. Gravity and normal use take their toll and the wires break off the solder pins. Can be fixed but it's often temporary. Any unit you see that's listed as broken will likely have this problem.
Feel free to ask any questions.

Great Ron!

Thank you for sharing!!

Here's a schematic I put together. Can someone check it and see if it looks right? This is just the buffer section as I figured no one was really interested in the pedal power supplies.

Well, I would be interested (or simply curious) to know about the pedal power supply somehow...

If you do have it, then feel free ! Thanks again for the schem...

from the picture - the pedal power supplies are four independent diode bridges feeding four electrolytics and four dc socket outputs.
not rocket science!
bajaman

bajaman wrote:from the picture - the pedal power supplies are four independent diode bridges feeding four electrolytics and four dc socket outputs.
not rocket science!
bajaman

Yeah, they're just your basic regulated supplies. There was a 12v supply but I changed it into a 9V.

There's also a .01uF cap across the AC supply I didn't add in.

bajaman wrote:from the picture - the pedal power supplies are four independent diode bridges feeding four electrolytics and four dc socket outputs.
not rocket science!
bajaman

I didn't look closely to these round things, and thus expected all bridge rectifiers to be squary devices...

Thanks bajaman, sharp eyes as always!

I know power supply is a common thing, but I -stupidly - assumed that these VHT ones were good quality ones as regards to the unit's price...

So there's no regulators in there... Can a simple filtering be good quality enough to get rid of residual oscillations in the voltage output? Are these VHT power supplies noisy??

If these are poor, I can't understand why they add them... If these are good, then what makes them efficient, 'cause I thought a regulator was the best way to get a clean DC?

ps: I'm actually into rockets (and gravity and satellites...) this week with some of my pupils, you know...

edit: thanks too ron... did you changed the 12V by tweaking a resistor to the 9V circuit values?

lolbou wrote:
So there's no regulators in there... Can a simple filtering be good quality enough to get rid of residual oscillations in the voltage output? Are these VHT power supplies noisy??

If these are poor, I can't understand why they add them... If these are good, then what makes them efficient, 'cause I thought a regulator was the best way to get a clean DC?


edit: thanks too ron... did you changed the 12V by tweaking a resistor to the 9V circuit values?

3 of the regulators for the pedal supplies are TO-92 sized 9v regulators. You can see them behind the power outputs.
The 12V was a TO-3 which I just replaced with a similar 9V unit.
I'll toss a schematic together and post it tomorrow.

I think I need my glasses.

I think I need some sleep.

As I can't have both at one time, I'll go for the second at once, and will come back with the first tomorrow...

Cheers Ron, and good night!

Thanks, Ron!
I might play with this. I like tube stuff.

Thanks for that schem EHMan!
I think you have a mistake on R5 and R6. C4 should probably be before them, otherwise they constitute a voltage divider with R3 and the anode of the first triode won't see the proper voltage.
I think their purpose is to attenuate the amplified signal before they hit the second triode, hence their probable location after C4.
Also, the succession of C5 and C6 seem strange.

Nyquist5 wrote:Thanks for that schem EHMan!
I think you have a mistake on R5 and R6. C4 should probably be before them, otherwise they constitute a voltage divider with R3 and the anode of the first triode won't see the proper voltage.
I think their purpose is to attenuate the amplified signal before they hit the second triode, hence their probable location after C4.
Also, the succession of C5 and C6 seem strange.

I checked it again visually and by continuity and the schematic is correct as far as R5, R6, C4, C5, and C6 go. I thought it looked strange, too.

...

Here's a merged image of both sides. Please let me know if you find an error.

What's the B+/HT and the measured input stage plate voltage?
Never saw one before but hoped it was a bit more "clever" then this for a dedicated tube buffer
Also does it really have R1 before the grid bleed resistor and not after like a normal grid stopper?
And that input cap... oy vey

I've been searching for a Valvulator schematic since mine is blowing fuses, those tiny cylinder plug-in's. They're not very common and have to be ordered. 250ma @250V. I was hoping a schematic would help make it easier than tracing the double sided circuit board. Help is greatly appreciated.... Mine is a Valvulator 1 with circuit board R1.2......

Update, I just tested it out on the bench. I ended up hooking up my meter set on ma AC in line with the AC cord. It's running fine, however, since I changed the 12ax7 it draws a lot at turn on. I put a EI 12ax7 and did you ever notice some European tubes glow bright when turned on? It's intial draw is more than the stock tube. Plus the fact I ordered fast blow instead of slo blow. So I'll order 300ma 250V slo blow fuses. Keep it mind if you change you tube...

At turn-on the heaters are cold, there is less resistance and so current draw is higher.
It's normal and happens with all heat type resistances... even light bulbs at home.
Mulards and Mulard style built tubes do flash harder at startup.
Maybe in the past they didn't care much because parts were cheap, but when ever I see my NOS Mulards flash it flips my stomach

There are ways to couter that current rush and old tube books sometimes do mention that issue, but I don't remember seeing "old" amps or schematics that implemented such methods.

crispycircuit wrote:Update, I just tested it out on the bench. I ended up hooking up my meter set on ma AC in line with the AC cord. It's running fine, however, since I changed the 12ax7 it draws a lot at turn on. I put a EI 12ax7 and did you ever notice some European tubes glow bright when turned on? It's intial draw is more than the stock tube. Plus the fact I ordered fast blow instead of slo blow. So I'll order 300ma 250V slo blow fuses. Keep it mind if you change you tube...

Back when I was a kid, and all my amplifiers were glass-mode types, it was common to put a resistor in series with the heater supply. This would limit the inrush current. There would then be a simple capacitor timer to operate a relay which would short out the heater resistor and give them full power. An even slower delay relay would then switch on the HT!

I modified a large number of AC30s like this, and was pleasantly surprised to see a well-known guitarist using one of mine a few weeks ago. The old "standby" HT switch was used instead for simple input muting as the application of HT was automatic.

mictester wrote:a well-known guitarist

with a well-known Red Special?