801a/vt-62 amp: looking for feedback

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paperhouse

New Member
Hi everyone--I've been lurking here for about half-a-year as I've gone further and further into the SET/single-driver wormhole. Right now I have a 2a3 amp driving a pair of Lowther PM6As in rear-loaded horn cabinets but have had this nagging sense of something being missing.

Not too long ago, I came across this VT-62 amp, being sold in Japan on an auction site. The price being low (apparently due to hum issues), I went for it somewhat impulsively and am now awaiting delivery. I can't help but wonder if I made a mistake and guess my ears will be the answer, but I'm wondering if any of you can tell me anything about what I'm getting into here. Driver tubes are 12au7, not sure about the rectifier nor the iron (the later of which I'm sure is crucial). Thanks for indulging me.

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Well, first off, the 801 is a beautiful tube. The output trannies looks a little dinky for good bass, but maybe it wasn't built for that. Anyway, it looks like it uses a two-stage, direct-coupled driver for each 801. DC filaments on the 801s, which you really need. I see two potential sources of hum. First, the 801 filament supplies may need more filtering. But possibly more problematic is that it looks like the B+ supply has very little filtering. I see two SS diodes, an input resistor and a pair of stacked electrolytics. Then there's a small gold axial electrolytic, probably to decouple the input stages. I'm looking for more filtering before the 801 plate supply and not seeing it. If that's the case, you'll need to add at least one choke and an extra capacitor or two before the 801 plates. Some Solen MKPs or something similar would fit easily. Hard to imagine anyone thought they could get away with that little B+ filtering in an SE amp. Can't tell if it's wireable for 120VAC but I don't know where you are.

Other than that it looks like you've got a fairly well-made little stereo 3wpc integrated SET amp that you ought to be able to modify into something decent.
 
zackthedog said:
Well, first off, the 801 is a beautiful tube. The output trannies looks a little dinky for good bass, but maybe it wasn't built for that. Anyway, it looks like it uses a two-stage, direct-coupled driver for each 801. DC filaments on the 801s, which you really need. I see two potential sources of hum. First, the 801 filament supplies may need more filtering. But possibly more problematic is that it looks like the B+ supply has very little filtering. I see two SS diodes, an input resistor and a pair of stacked electrolytics. Then there's a small gold axial electrolytic, probably to decouple the input stages. I'm looking for more filtering before the 801 plate supply and not seeing it. If that's the case, you'll need to add at least one choke and an extra capacitor or two before the 801 plates. Some Solen MKPs or something similar would fit easily. Hard to imagine anyone thought they could get away with that little B+ filtering in an SE amp. Can't tell if it's wireable for 120VAC but I don't know where you are.

Other than that it looks like you've got a fairly well-made little stereo 3wpc integrated SET amp that you ought to be able to modify into something decent.
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Appreciate the response and the knowledge, Zack. It's reassuring that the build looks fundamentally sound, and I'll see just how bad the hum is. Dead silence isn't a high priority for me, but are there other potential consequences to the lack of B+ filtering? I'm in the States so will be seeking a voltage transformer but it would definitely be ideal to rewire it for 120 if possible.

I clearly have some homework to do, but from what I understand, high impedance output transformers are desirable for 801a amps. If they do sound dinky and I replace them, will I need to match the impedance on the present ones? Not sure I'll have any way of knowing what they are unless I can manage to communicate in broken Japanese with the seller (I used a proxy bidding service so haven't interacted with him or her.)
 
paperhouse said:
Appreciate the response and the knowledge, Zack. It's reassuring that the build looks fundamentally sound, and I'll see just how bad the hum is. Dead silence isn't a high priority for me, but are there other potential consequences to the lack of B+ filtering? I'm in the States so will be seeking a voltage transformer but it would definitely be ideal to rewire it for 120 if possible.

I clearly have some homework to do, but from what I understand, high impedance output transformers are desirable for 801a amps. If they do sound dinky and I replace them, will I need to match the impedance on the present ones? Not sure I'll have any way of knowing what they are unless I can manage to communicate in broken Japanese with the seller (I used a proxy bidding service so haven't interacted with him or her.)
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I agree that a dead silent SET amp is a difficult achievement. ;-). Technically there's no harm with the lack of adequate filtering but that's probably where the hum is coming from. It's not a big deal to correct, less than $100 worth of parts. You definitely want at least 8K primary OPT for the 801. I wouldn't worry about them, if they sound good it doesn't matter, but a replacement would be a good 10W SE OPT for an el84 or similar. Shouldn't be hard to upgrade them if you want to.

Basically it looks pretty workable, I just don't understand why there isn't a proper CLC (Cap-choke-cap) filter in place. It really needs it.

ETA: When you get it you want to look at the power tranny, diode arrangement to figure out how he's done it, and check the B+ voltage so you can be sure to duplicate it.
 
zackthedog said:
I agree that a dead silent SET amp is a difficult achievement. ;-). Technically there's no harm with the lack of adequate filtering but that's probably where the hum is coming from. It's not a big deal to correct, less than $100 worth of parts. You definitely want at least 8K primary OPT for the 801. I wouldn't worry about them, if they sound good it doesn't matter, but a replacement would be a good 10W SE OPT for an el84 or similar. Shouldn't be hard to upgrade them if you want to.

Basically it looks pretty workable, I just don't understand why there isn't a proper CLC (Cap-choke-cap) filter in place. It really needs it.

ETA: When you get it you want to look at the power tranny, diode arrangement to figure out how he's done it, and check the B+ voltage so you can be sure to duplicate it.
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Great info and thanks again!
 
PakProtector said:
A 12AU7 with an 801? Sacrilege, or incompetence amounting to it.
cheers,
Douglas
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Hi Douglas--I have read comments to the effect that the 12au7 produces a somewhat thin sound with 801s, even though people do seem to use it. Are you aware of any alternatives that might be implemented without too much pain?
 
SE10/801A > Lowther = great combo!

Consider replacing the 12AU7 with a 6CG7 which is essentially a 9-pin 6SN7. Are the output transformers Noguchi Finemets by any chance?
 
setup1 said:
SE10/801A > Lowther = great combo!

Consider replacing the 12AU7 with a 6CG7 which is essentially a 9-pin 6SN7. Are the output transformers Noguchi Finemets by any chance?
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They sure look like the FM-6WS. Thanks for the link, that's encouraging! And for the 6C67 suggestion, looks promising.

Edit: Hopefully they're the FM-GWS-H, which have higher primary impedance...
 
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My dearly departed friend, Brian Clark's mono system. He used an SE801A amp to drive his Lowther TP-1.

SE10-1.jpg

I built this Stereo SE10 amp 20 years ago and loved the way it sounded driving a pair of Brociner TP1s. Alas, I couldn't afford the speakers so I ended up selling the amp.

But I've been saving a single Tamura F7004 to build another SE10 amp for my mono system with DC on the filaments.

JE
 
paperhouse said:
Hi Douglas--I have read comments to the effect that the 12au7 produces a somewhat thin sound with 801s, even though people do seem to use it. Are you aware of any alternatives that might be implemented without too much pain?
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Type 5687 comes to mind. The Russian 6H6Pi is IME, just a wee bit cleaner than some 5687's( the type 5687 has many variants, the 6H6, not so much ). Type ECC99 will plug right in, and type 12FV7( 5?) is another high gm, medium mu. All these take about 3x the heater current of a 12AU7...so proceed with some caution.
cheers,
Douglas
 
setup1 said:
My dearly departed friend, Brian Clark's mono system. He used an SE801A amp to drive his Lowther TP-1.

I built this Stereo SE10 amp 20 years ago and loved the way it sounded driving a pair of Brociner TP1s. Alas, I couldn't afford the speakers so I ended up selling the amp.

But I've been saving a single Tamura F7004 to build another SE10 amp for my mono system with DC on the filaments.

JE
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Beautiful looking amps, and I'm sure those Lowther Tp-1s were amazing. Thanks for sharing!

PakProtector said:
Type 5687 comes to mind. The Russian 6H6Pi is IME, just a wee bit cleaner than some 5687's( the type 5687 has many variants, the 6H6, not so much ). Type ECC99 will plug right in, and type 12FV7( 5?) is another high gm, medium mu. All these take about 3x the heater current of a 12AU7...so proceed with some caution.
cheers,
Douglas
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Appreciate the suggestions, I'll look into those.
 
Just an update: the amp arrived. It was meticulously packed--have to love the Japanese attention to detail. Dinky power cord hard-wired to the amp, but oh well.

I put in the tubes, plugged it into a cheap voltage transformer, and turned it on. The hum is not bad at all--quieter, actually, than my 2a3 amp. So then I turn on the music and--ugh, not good. "Tube-y" in the worst way. "Well, a fool and his money are soon parted" I told myself as I prepared to plug my old amp back in. But then I decided, well, I might as well try using it without the voltage transformer, since it's not going to fry the amp.

Running directly from the wall outlet, the difference was huge. There's a palpable sense of energy across the frequency spectrum that wasn't obvious with my 2a3 amp, especially after I replaced the stock Hytron 801s with a pair of 1940s-vintage Sylvanias. Significantly more raw volume too. The dimensions on the output transformers and wire colors seem basically the same as Noguchi Finemets, so I'm assuming that's what they are.

There is bit of messiness around the lower midrange and bass, which I'll see if rolling driver tubes fixes. I have 12au7 to 6cg7 converter sockets on the way as I'm not quite ready to brave the wiring.

Now, to solve the pesky voltage conversion issue. I'm just surprised how radically the voltage transformer messed up the sound.
 
It looks like your power transformer has a multi-tapped primary. Check if the seller already wired it for 120V.

paperhouse said:
The dimensions on the output transformers and wire colors seem basically the same as Noguchi Finemets, so I'm assuming that's what they are.
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It seems like there's enough slack in the OPT leads, try removing the mounting screws and take a peek underneath the transformer. There is a sticker with the model number in mine.

JE
 
setup1 said:
It looks like your power transformer has a multi-tapped primary. Check if the seller already wired it for 120V.



It seems like there's enough slack in the OPT leads, try removing the mounting screws and take a peek underneath the transformer. There is a sticker with the model number in mine.

JE
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Turns out there wasn't enough slack to take a peak. I'll take a look under the hood once I've made sure I won't electrocute myself. If I'm not mistaken, this looks to be the power transformer: https://www.gtrans.co.jp/SHOP/PMC-3520HG.html . I doubt the seller wired it for 120v since he didn't know it would going to the States, but should it be possible given the specs? Apologies if the page doesn't auto-translate.

This thing does sound amazing. The hum is down to very little after I moved my equipment around a bit. People weren't kidding about the synergy with Lowthers and 801s. It's a bit counter-intuitive because they both emphasize the upper end, but whereas there was some shrillness before, now it just sounds right (with the appropriate EQ added.)
 
I have auto translate for Japanese in Chrome. Looks like I was mistaken, it only has a 100V primary winding. Be careful plugging directly to a US outlet, since the 20 volts difference can make or break the amp. Did you check if your 120>100V step down is really stepping down 20 volts?

I had a friend who bought a JDM Morikawa SE2A3 which came with a step-down transformer. He loved the amp but was getting popping sounds after 20 minutes of listening. I took the amp home and found nothing wrong with it in the test bench and and also in my system plugged to my Variac set at 100V. It turned out his transformer, was passing 120V.:(Good thing he also has a Variac. No problems since then.:)

Some nice reading on the 10/VT25/801A triode, you probably know this already. And here's a pdf of a 1920s RCA tube manual, the type 210 tube data is on page 24.
 
setup1 said:
I have auto translate for Japanese in Chrome. Looks like I was mistaken, it only has a 100V primary winding. Be careful plugging directly to a US outlet, since the 20 volts difference can make or break the amp. Did you check if your 120>100V step down is really stepping down 20 volts?

I had a friend who bought a JDM Morikawa SE2A3 which came with a step-down transformer. He loved the amp but was getting popping sounds after 20 minutes of listening. I took the amp home and found nothing wrong with it in the test bench and and also in my system plugged to my Variac set at 100V. It turned out his transformer, was passing 120V.:(Good thing he also has a Variac. No problems since then.:)

Some nice reading on the 10/VT25/801A triode, you probably know this already. And here's a pdf of a 1920s RCA tube manual, the type 210 tube data is on page 24.
Click to expand...

Thanks for looking at that, and for the links. Whatever my step-down transformer is doing, it sounds terrible! I'm going to try a Variac see if it improves things--hadn't heard of them, so thanks for that idea too!
 
It finally clicked for me that you're the JE of JElabs--thanks for the great blog, and for providing valuable info about the Japanese audio world! I actually spent some time in Japan myself, but in Zen monasteries, so there obviously wasn't any audio equipment around.

There wasn't any identifying info underneath the OPTs, and I'm realizing that the dimensions are a bit different from the Noguchi Finemets--about as tall, but a little bit wider and significantly more deep. Also, the wires coming out the front are white, red, and brown, whereas all the single-end Noguchis seem to be orange, red, brown or yellow, orange brown (thanks for the kanji color chart, by the way.)

The only trannies I've seen that look similar are Kasugas, but those are even smaller. Since the power transformer is clearly Noguchi, seems likely these are too, but maybe they're a custom build? Ah well, it sounds good, just have to restrain myself from listening to it until my (hopefully) better voltage transformer arrives (I ended up ordering a Nissyo.)
 
paperhouse said:
It finally clicked for me that you're the JE of JElabs--thanks for the great blog, and for providing valuable info about the Japanese audio world! I actually spent some time in Japan myself, but in Zen monasteries, so there obviously wasn't any audio equipment around.

There wasn't any identifying info underneath the OPTs, and I'm realizing that the dimensions are a bit different from the Noguchi Finemets--about as tall, but a little bit wider and significantly more deep. Also, the wires coming out the front are white, red, and brown, whereas all the single-end Noguchis seem to be orange, red, brown or yellow, orange brown (thanks for the kanji color chart, by the way.)

The only trannies I've seen that look similar are Kasugas, but those are even smaller. Since the power transformer is clearly Noguchi, seems likely these are too, but maybe they're a custom build? Ah well, it sounds good, just have to restrain myself from listening to it until my (hopefully) better voltage transformer arrives (I ended up ordering a Nissyo.)
Click to expand...

It's a pleasure to share my audio adventures! :)

Your OPTs may also have been manufactured by Toei which had a stall in Akihabara Radio Center when I visited in 2015. If memory serves me right, Toei had a website then but google didn't yield anything now. I hope that company wasn't another recent casualty.

Stay safe and listen to music to pass the time!

JE
 
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