# Acetone 301 help



## SteveAppleton77 (Jun 26, 2020)

this amp has popped up once or twice in the past. It’s a bit of an odd ball I think. It has an odd, super impossible to find 50hb26 power tube. Fortunately for now that’s not my issue. Maybe later. 
To start, I’m trying to add in a three prong power cord. The layouts a little strange to me. It’s a two prong cord of course. But no death caps at all, which worries me a little. The power tranny wires are not colours I’m used to. 
I drew it out. Hope it’s legible. And I’ll add a pic too. 
Any ideas??


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## Lincoln (Jun 2, 2008)

It will be interesting to see what the techs have to say about this one. 
That "50" on the front of your "50HB26" power tube, tells me this amp doesn't have a power transformer. Also noticed the chassis is being used as a ground. You need an expert opinion on this one as there is a potential for electric shock. An isolation transformer may be required. Normally, you would remove the toggle switch from the white wires (joining them) and run the black wire though the toggle instead. Green to the chassis.


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## SteveAppleton77 (Jun 26, 2020)

I’ve read about those widow maker amps. This one has a power tranny. Granted it’s use of a 50v power tube is unusual. Nothing compatible at all. I hope it’s still good!
I think I see the direction your going with wiring.
The two whites and other side of pilot light together. 
Black to fuses then to switch.
Then the yellow, orange and pilot wires off the other side of swicth?


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## Lincoln (Jun 2, 2008)

Very strange. Yes, that's where I would head. Take the white wires off the toggle switch. Connect the two white wires together with the 100K resistor to the pilot lamp. Run the black wire from the cord to one side of the toggle switch. Run another piece of black wire from the other side of the toggle switch, down to where the black wire originally went to the fuses. Fuses can go either before or after the power switch. The important thing is to get the switch into the black wire circuit and out of the white wire circuit. New green wire to the chassis. Green wire should be the longest of the three, so it would be the last pull out should the cord go one direction while the amp is going another direction.

One of the guys I hung with growing up had an Acetone amp, looked very much like that one. First spring reverb I ever laid eyes or ears on.


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## alwaysflat (Feb 14, 2016)

You probably should have a schematic before you go an start grounding, A floating chassis on some amps when grounded, can interfere with operation, depending on design. An isolation transformer up front would be your best solution to maintain original circuit operation and give you the safety factor you're looking for.


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## dtsaudio (Apr 15, 2009)

It is quite likely, that even though there is a power transformer, the output tubes filaments are wired in series and run directly off the line. In most of Japan (where this tube originates) the AC is 100V/50Hz. Putting the two in series will yield 50V across the filaments. It is also probably not referenced to the the chassis, so it is floating. This is potentially a dangerous situation, so be very careful.
There must be something about the primary that allows for other voltages. Which is why there are two fuses. I don't think both fuses should be in there. Only one is necessary, but you need to know what winding to fuse.
This is a schematic to the power inlet of one of Acetone's other amps. You can see the filaments on the 100V part and a switch to change primary voltage.
Other than that Lincoln is correct. However I always fuse before the switch. That way it is protected as well.


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## SteveAppleton77 (Jun 26, 2020)

Ok so my last Cap finally came in. Puerto Rico to Canada for one Cap. All Caps and a couple of resistors now changed. Two new 12ax7s. Fired it up and it does play. A little bit of hum. The hum is always there with or without guitar/cable plugged in or volume on zero. It does get louder as the volume is turned up. On the bright side the power tube does not look like it’s red plating anymore.

I sorted the new power cord and decided to just wire it in just as it was before, but with the green to the chassis. As for the fuses. On the chassis near the fuses it actually says 100v and 117v. This fits with what your saying dtsaudio. So as I’m in Canada I’ll use the 117 side. I guess it was done be able to be used in China and North America.

The tremolo works great but no reverb. I’ll have to dig into that one. Maybe the tank is toast.

I took some measurements off the heaters. The power tube is right at 50 as it should be. The two 12ax7s though are sitting too high. Actually twice the amount they should be, at 12.5ish vac each. I’m going to go out on a limb and guess this is where my hum is coming from. I’m a little lost on this one. The power for the preamp heaters get it from a tap off the tranny directly. Haven’t even touched that area of the circuit. Did preamp tubes run hotter in the 60s?

Weird that it’s perfectly twice the amount. There’s something to that.

The wiring for them is different then I’m used to as well. Only one wire off the tranny to the first preamp heater tab, the second heater tab runs to the the second preamp tube heater tab then the other tab to ground? I’m guessing that puts them in series? Could this be where the double the amount is coming from? Strange though. This is the original wiring. 

Any thoughts guys? I’m so close.


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## jb welder (Sep 14, 2010)

For series wiring the heaters run at 12.6V each. They can also run parallel at 6.3VAC each which we are more accustomed to seeing. The first number of the tube is the heater voltage. But for the dual triodes (12xxx) they have 2 separate 6V heaters which can run in series or parallel.
So your heater voltages are good.
Single ended amps (one power tube) tend to hum more because you don't have the humbucking effect of a push-pull power amp. So that could be the hum you hear even with the volume down.
You may be able to tame that part by altering the power supply but the difference may not be much.
The hum that increases as you turn up the volume would be something else, something coming in before the volume control in the circuit. Sometimes just moving wires around in the input area can help (lead-dress).


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## SteveAppleton77 (Jun 26, 2020)

Gez I had been dealing with the power tube and had learned that the 50 in its name (50hb26) was its heater voltage. How did I not make the connection to the preamp tubes? Glad these forums are here.
The heater wires are glued to the chassis but I may try to elevate them. 
I’m wondering if the hum maybe coming from the old power tube? There’s no way to swap to test. I have heard that can swap in a 6l6, but will need a new socket and filament transformer. As the tube is older then I am and will inevitably need switching I may just get it over with.


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