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Old 26th April 2003, 09:54 AM   #1
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Default ASL wave 8 monoblocks

Hello everyone,

Just ordered a pair of these (I like the mechanical design, the electronic design is the usual ecl82 first stage, concertina phase splitter and a pp output stage), anybody had a chance to listen to them, and/or modify them?

Any info will be appriciated.

Thanks.

Glass_painter
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Old 26th April 2003, 03:22 PM   #2
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There are several posts on this in Audio Asylum, maybe they've been discussed here as well. Replacing the coupling caps with Auricaps and using Svetlana tubes appear to be the most popular mods to these. I've also replaced the PSU caps with Panasonic TSHA/TSHB, added a "snubber" on the B+ supply, and rerouted the ground connection on the heater wiring. One of my Svetlana tubes (old Russian military stock bought on eBay) died while trying to clean the pins, so I'm back to the stock Ei tubes. The Svetlanas hummed much more too, I don't know why.

I think they sound pretty good, but I don't have any prior experience with tubes, so I have nothing to compare them against.
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Old 26th April 2003, 04:08 PM   #3
Morse is offline Morse  United States
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Hi Saurav;

>>>...The Svetlanas hummed much more too, I don't know why...<<<

Interesting. I'm getting into the 6BM8 on my latest DIY amp that's under construction, so it's of some importance over here.

Does the ASL Wave 8 use AC or DC on the heaters? If there's a difference between cathode and heater voltages, that can cause 'hum' in AC heaters. IIRC Svetlana 12AX7's are not recommended for amps with AC heating either.

If it's a real bother, you could always add a rectifier board for the heaters. It needn't be more than a bridge rectifier and a 2200uF 16V cap.

All the best,
Morse
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Old 26th April 2003, 05:50 PM   #4
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Quote:
Does the ASL Wave 8 use AC or DC on the heaters?
I'm pretty sure it's AC.

Quote:
If there's a difference between cathode and heater voltages, that can cause 'hum' in AC heaters.
Good point which I hadn't considered. I'll have to look at the schematic again. I know it has the R+R to ground for the noise currents, but I don't remember seeing a voltage divider to bring the heaters up close to the cathode voltage. How does that work anyway on a multiple-section tube like the 6BM8? The cathodes of the triode and pentode sections could be at pretty different voltages, so which one do you set the heater voltage for?

With the Ei tubes, I can't hear the hum from my seating position (about 8' away from 96dB speakers), so I haven't fretted over it too much. The Svetlanas hummed quite a bit more, and I think those would have been audible. However, I used old Russian stock, and I think Svetlana produced (or still produces) 6BM8s very recently, so those might behave differently.

Try this link for a schematic for the Wave 8s. For some reason, linking directly to the image doesn't work.

http://hifiaudiolabs.tripod.com/waveav8info/
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Old 26th April 2003, 06:47 PM   #5
Morse is offline Morse  United States
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Hi Saurav;

>>>...The cathodes of the triode and pentode sections could be at pretty different voltages, so which one do you set the heater voltage for?...<<<

Good question. The more vulnerable cathode is the one on the small signal triode, since the amount of induced hum in that cathode to the signal will proportionately be larger than the amount of hum induced in the output pentode's cathode with respect to the signal there. Since the small signal triode is only floated by +.6V, it could just be that the valve is particularly vulnerable to AC heater induced hum - definitely I'm going to use DC on mine after reading this (I have 4 Svetlanas and 4 Ei's on hand so I want to be able to work with either).

It's a trickier question when you have something like a SRPP. Some people will use 2 filament windings, each floated separately and split the functionality of the circuit so that all the "high" cathodes are on one dual triode and all the "low" cathodes are on the other. If I decide to use a single filament winding (being a penurious audio nut), my own rule of thumb is to split the difference between the two voltages for the heater. That's the approach I used on my 2A3 (which uses a cathode follower with one cathode set much higher than the other).

Of course this is all coming down to a "if in doubt use DC" type of thing (assuming that the valves heaters are AC/DC compatible - the 6BM8's are, according to the Svetlana tech sheet at their website). And also assuming that you're not exceeding the max cathode/heater voltage limits.

As usual, just my 2 pence worth!

By the way, what 96dB speakers are you using?

All the best,
Morse
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Old 26th April 2003, 07:29 PM   #6
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I also wondered if the Svetlanas might be more susceptible to picking up hum from the transformers... don't know if that's a possibility.

My speakers are sealed Adire HE12.1s.

Click the image to open in full size.
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Old 26th April 2003, 09:24 PM   #7
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Default BS.

Hi,

Quote:
If there's a difference between cathode and heater voltages, that can cause 'hum' in AC heaters. IIRC Svetlana 12AX7's are not recommended for amps with AC heating either.
Totally not true.

Get your act together guys.

Tsssh, the stuff I read here....

Cheers,
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Old 27th April 2003, 02:03 AM   #8
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There is a cathode-heater breakdown voltage that should not be exceeded. That probably has nothing to do with hum. However, I've also read that in voltage gain triodes, the cathode might pick up hum if the heater is negative w.r.t. the cathode, and I've seen designs which keep the heater at a slightly higher potential than the cathode, by using a voltage divider from B+ to ground. Are you saying that that's not true, and the voltage divider isn't needed?

Or maybe you were commenting on the statement about Svetlana 12AX7s. It's not too clear from your post.
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Old 27th April 2003, 02:36 AM   #9
Morse is offline Morse  United States
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Hi guys;

As far as the Svetlana 12AX7 is concerned, I'd swear I'd read that about it somewhere - but now I can't find it (embarrassment reigns supreme at the moment).

And, maybe I'm wrong about there being a correspondence between high heater/cathode voltages and AC hum pickup, but I've got a JAN Philips 12AX7WA that sure follows that rule. Darned if I know where I first read a claim of that correspondence, but it was a "oh that's what's causing this" kind of moment. If that's not it, I'm darned if I know.

Anyway, if it's the worst mystery I ever face or the worst mistake I ever make, I'll live with it. Sorry to hand out questionable info.

All the best,
Morse
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Old 27th April 2003, 08:19 AM   #10
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Default HUM.

Hi,

Quote:
As far as the Svetlana 12AX7 is concerned, I'd swear I'd read that about it somewhere - but now I can't find it (embarrassment reigns supreme at the moment).
What you may have read is that the SOVTEK 12AX7LPS sports a special S "spiral wound" filament to prevent hum when AC fed on the heaters.

Quote:
There is a cathode-heater breakdown voltage that should not be exceeded. That probably has nothing to do with hum.
This is correct.
The voltage is almost always stated in the datasheets, usually in the 120 to 150 V range.

When you do exceed it you will have some HF coupling and you risk that the heater and cathode will "stick" causing a short.

Quote:
Are you saying that that's not true, and the voltage divider isn't needed?
No, that's not what I'm saying.
Biasing the heaters is good practice, wether the tube is AC or DC heated is not relevant though.

Hope this clarifies it a little,
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