Test with Russian "6n14n" 6BQ5 tubes in Peavey Bravo amp

[tonepoet]

You may have seen these Russian military 6BQ5/EL84 style tubes with Russian writing that looks like 6n14n and CCCP on them. You can pick them up pretty cheap on eBay. I got a matched duet to experiment with for only $7.99

First, the seller said they are "lightly used military tubes" and they did test like new on my tube tester. Very strong.

Secondly, when examined side by side with the Sovtek EL84s that came stock in the Bravo, they are identical in build characteristics.

In the amp, they sounded identical to Sovtek EL84s, but there is one difference. These things run really hot!

Now, as you may know, the Bravo has the tube section enclosed inside the chassis with a small cooling fan. At one point I walked up to the amp to tweak a knob and smelled a hot, burning smell. I touched the top of the amp cabinet and it was HOT. I shut the amp off, took the chassis out and there was no sign of burning inside the amp. I put the original tubes back in, played for hours and just one small area of the cabinet top over the tubes was slightly warm.

So, I would say that these tubes, if used, should be well ventilated. But, if you like the sound of Sovtek EL84s, they look like a cost effective alternative.

[loudthud]

Did you adjust bias or just plug and play? It's not easy to measure heater current, but would you measure the resistance of the heater cold and compare to the Sovtek?

[tonepoet]

@loudthud, I just did a plug and play. I'm new to the Peavey Bravo, but unless I'm missing something, I'm not seeing a bias adjustment on the schematic. I'm heading over to my rehearsal space now. I'll measure the resistance on the heater.

[bob p]

Last night I dropped a pair of JJ EL84 into a little HiFi amp that had a pair of old Mullards in it. When switching the amp on I noticed a bright flash of light emanate from the heaters, which subsequently went dim, and then came back up again a few seconds later. I hadn't noticed any flashes on power-on before. At idle the glow from the heaters looked a lot brighter with the JJ than with the old Mullards, and my Kill-A-Watt indicated that the amp was drawing about 5 more watts at idle. Granted, this could have been due to non-equivalent bias, but it was late so I didn't have time to look into the matter last night. I'll try to do that later tonight. I just thought I'd ask if it's typical for eastern Europoean tubes like these to have higher heater current demands than their "equivalent" western tubes.

[kleuck]

The JJ were known to draw more current yes, but actually, MOST modern EL84 are drawing more than 760 mA.
I used to have 6P14P, and indeed they were getting very hot (in a cathode-biased amp) but i can't remember if it was a bias or heater issue, i switched to 6P14P-EV, they run "colder" in the same amp.

[tonepoet]

@loudthud - Here's what I measured with my multimeter and, since I was in there, I measured cathode and plate current and got the following:

Russian 6n14n Tube A Tube B
Heater ohms 2.5 2.9
Cathode ma 16.0 14.2
Plate ma 14.4 12.8

Sovtek 6BQ5 Tube A Tube B
Heater ohms 2.5 2.5
Cathode ma 18.7 16.0
Plate ma 17.0 14.4

I can tell you that those 6n14n tubes are much hotter to handle after just a minute or two on.

[tonepoet]

well, I see trying to make columns for the data didn't work out so swift, but I guess you'll see what I've listed there.

[Bruce / Mission Amps]

Almost every one of those Russian "military" 6BQ5 tubes I've tried always ran 20-35% hotter then any other new EL84s if tried in the exact same circuit.
Not sure why but that is the facts and I probably have 100 of them.
Rebias them down to about 10 watts each and they sound very good.
I'm not convinced they are a better "deal" then stock JJ EL84s though... especially when considering the extra handling of redoing the cathode circuit if the amp is not fixed bias with an adjustable bias supply.

[tonepoet]

Gotcha. I am running JJs in my Peavey Classic 30 and like them a lot and I have some on the way for the Peavey Bravo. Thanks.