807 Audio Amp Progress Report

[tubelab.com]

Ok, my memory isn't what it used to be, so I looked at the tubes.The Sovtek logo is in black. The text reads 6SN7GT SOVTEK Made in Russia. This is printed directly over the Russian manufacturers logo. Under that it reads 6H8C 8810.

[Miles Prower]

^^^^^^^^^

That's what mine look like.

[kevinkr]

I have a bunch of 6H8C with about the same date codes. They certainly look different than the US made 6SN7 I have, but they don't sound bad.

As I recall (might be mistaken) the equivalent of the 6SL7 is the 6H7C and these are ok as well.

I wonder if anyone is actually making new ones, from what you describe it sounds like new sensor is just relabeling these old stock tubes.

Kevin

[tubelab.com]

I didn't mean to imply that they sound bad, just different than many that I have tried. One of the dislikes that I have with 6SN7's is that many are microphonic. The Sovteks are the least microphonic of the bunch.

[Miles Prower]

I wonder if anyone is actually making new ones, from what you describe it sounds like new sensor is just relabeling these old stock tubes

It looks like they're relabeling the 6SN7s. However, the 6SL7s that I got from them look like these were newly manufactured. There aren't any old logos, or evidence of erased old logos.

So far as the Sovtek 6SL7s, these don't seem to be terribly microphonic, as sharply rapping the 6SL7 doesn't cause very much disturbamce to the output on the o'scope. The 6J5 NOS Westinghouse is slightly worse in this regard, but still any disturbance isn't really all that apparant. Nothing to complain about here.

Once the driver is complete (uses 6SN7s as followers) we'll see how well these perform. So far, nothing to complain about the Sovtek's I've tested.

[tubelab.com]

I have a Motorola branded (they didn't make their own tubes) 6SN7 that is so microphonic that the amp howls when you turn it up, and you can actually talk to it and hear yourself in the speakers. These tests were done in a line stage so there is plenty of gain after the tubes.

I have used Sovtek tybes for several years with generally good results. I think that I have abused several 6550's in guitar amps and they took far more than they should have. Unfortunately I had bad luck with their 300B's a few years ago and New Sensor's attitude convinced me not to buy any more of their tubes.

[Miles Prower]

Unfortunately I had bad luck with their 300B's a few years ago and New Sensor's attitude convinced me not to buy any more of their tubes.

I remember that. Pretty poor customer relations, for sure. I wonder if they ever fixed that problem with the 300Bs? Not that I particularly care since that's a "cult" tube and a glorious ripoff. There are other triodes and trioded pentodes that'll work as well, or better. When I do a triode project, it'll be with trioded P-P 6V6s. For a SET project, probably one of the xmtr triodes. (I'd like to get an 806 for that.) No sense in getting ripped off for some "boutique" tube.

[tubelab.com]

I got caught up in the 300B madness several years ago, a few years after I started building tube amps again. I spent way too much money on 4 of them to build a push pull amp. The amp sounded great though, and I was beginning to believe the hype. Then the first tube failed. I bought another one, the amp sounded good again, then poof. I gave up on 300B's and put the amp in the closet and bagan to rob it for parts.


That amp sat in the closet for at least a year, missing the choke and a filament transformer. Then one day I was at the Miami hamfest and I saw some Sovtek 300B's cheap. I knew the seller and he said that if I didn't like them he would refund my money. 5 tubes for $100 with a money back guarantee, how could I lose. Well that was 3 or 4 years ago, I rebuilt the amp, I still have it, and it still sounds great. I have built at least a dozen amps since then and the 300B push pull amp still has a certain slam to it that my other amps don't have. Music with large transients like rock and techno just jump out at you.

I usually like to design amps around tubes that I have (and I have plenty). I don't put much faith in the "audio hype" mentality, but I think that the 300B and the 45 have some merit. I have recently built some SE amps (the Tubelab SE) using the new Chinese 300B's and NOS 45's because I have had paying customers request them. I must admit that they sound good, especially the 45.

At the request of someone on this forum, and to verify an old rumor, I wired a 6AV5 sweep tube into the Tubelab SE. The old rumor (now verified) says that Sylvania was selling 6AV5's, triode strapped as 6B4's. Well the 6AV5's sounded good, really good, better than the audio snob triodes kind of good. In my usual style I really cranked these tubes, cranked them till they glowed, and they really sounded good.

Then I started trying other tubes in the same amp. 6V6's, 6L6's, and various sweep tubes, all triode wired. The 6V6's did sound good too. That is when I picked up the 807's from the warehouse, and they are still sitting on the bench.

I believe that a good tube amp designer can make a decent sounding amp out of almost any power tube, if you take the time to find its sweet spot. The 300B has a pretty large sweet spot. Almost anybody can make a good sounding amp with them. Maybe that is part of the hype.

An 806, I hadn't heard of that one, so I looked it up. I definitely don't have anything like that in the warehouse. But I do have about 20 833A tubes. Initial experiments reveal that this tube ROCKS!

[Miles Prower]

I think that the 300B and the 45 have some merit. I have recently built some SE amps (the Tubelab SE) using the new Chinese 300B's and NOS 45's because I have had paying customers request them. I must admit that they sound good, especially the 45.

Unforch, you don't get much power out of a 45. They do look good as drivers. Although the spec sheet says you can get 20W with AB2 45's. Perhaps that would work as well?

An old article in one of the earlier ARRL handbooks did claim that the vertical and horizontal power amp tubes worked especially well, so far as low distortion and linearity. That's why so many appeared in RF linear amps. There are a whole bunch of those still available at reasonable prices. Some $300.00 for 300B's isn't reasonable.

[tubelab.com]

I know that I am not going to spend $300 for a 300B. Those prices ARE created by the audio snobs who are responsible for establishing the "boutique status" of certan tubes, and certain BRANDS of tubes. You can get the new Chinese 300B's for $45 each if you know your tube broker real good. That is at the extreme upper end of my budget. Some of my amp customers have asked for WE 300B's. I will build the amp with the Chinese ones and let them source their own tubes. I don't want to be in the middle when a $300 tube dies!

I have not tried P-P 45's. I tend to use these as drivers. I find that you can but "weak" ones on Ebay for under $10 each. They might not sound great trying to pump 2 watts into a speaker, but they work well when loaded by a CCS and buffered by a mosfet.

I have had great success with sweep tubes, both horizontal and vertical. These are still cheap, except for the ones that were popular in CB amplifiers. Most of those things ate tubes faster than a guitar amp, and the supply is getting thin. Just price a NOS 6JE6C/6LQ6, they cost almost as much as 300B's. My favorite is the 6LW6, these have an octal base and the biggest plate structure that I have seen in a receiving tube. I have had no problem getting 140 Watts RMS out of a pair. You used to be able to get these on Ebay for $5 to $10 each. Then there was a cunstruction article in Glass Audio featuring these tubes, now they are $20 each.