Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by DIXØN, Jun 30, 2008.
Can you replace the former with the latter, as long as the bias is re-set?
According to my amp tech and Paul Rivera no. It has to do with the impedance of the output transformer. I'm not sure what the ill effects will be.
There is no generic answer to that question.
You have to tell us which amp you're thinking of.
6V6's draw 450mA. EL34's draw 1.5A
I don't know of ANY production amp that has a PT with that much reserve filament current on tap.
Yes, we need to know what amp is being discussed here, but all the same: I'm >98% sure the answer will be "no, you can not replace the former with the latter."
What Mark said.
I'm trying to convey that you should list ALL pertinent details in your posts so we don't have to go through 6 posts to get them
Just FYI, here's one amp where it seems possible:
EL34's have pins 1 & 8 grounded... 6v6's designs usually only have pin 8 (cathode) grounded. Plz correct me if I'm wrong, but I thought two el34's and two 6v6's were appromately the same primary imp = 6-7k ?? So you could sub el34's for 6v6's if the PT could handle an EL34's current requirements.
Impedance would be the least of my concerns.
In addition to my previously-voiced concern about filament current (which, IMO, is a deal killer tight there)......yes, a 6V6 has the suppressor internally tied to the cathode, both of which terminate on pin 8. Pin 1 is typically not needed by the tube and is often used by the amp maker as a terminal point.
If an amp has it's socket so wired, the direct insertion of a EL34 would be a problem. EL34's do NOT internally tie the suppressor, but rather terminate it discretely at pin 1. So whatever the socket is using pin 1 for....that electrical circuit will be presented to the 34's suppressor. Not good.
The Emery Superbaby can handle both, no biasing necessary. I made this exact swap about a month ago, but have since gone back to the 6V6 setup.
It's an old Laney AOR 30 head I got off eBay, it has no valves and the transformers are buggered, so the PT issue is no longer an issue. However, the spec for 6V6s says that a pair only gives 15W, so thought I'd replace with EL34's for a bit more power. Plus EL34's seem to be cheaper where I look.
I've got a cathode biased output in a 2204 design, with an Eico output transformer, designed for an EL84 pair. It works great with 6V6's, 6L6's and 6550's. With EL34's however, the crossover distortion is very bad. The 34's have a different need in the area of control grid to cathode voltage difference. They run cold in that configuration. That's all I got!
What's wrong with the transformers? More than likely, if the amp is supposed to use 6V6s they'll be totally buggered if you plug in EL34s.
There's no way I would even try EL34s without first proving that it works with the correct tubes. If you jump straight to EL34s you'll have no idea why it failed, if it fails.
I've got that combo with 2x6V6. The manual says class a (30 watts). I doubt that, but I have mine in a 2x12 combo cab with a Greenback and a G12-65 and it's LOUD ! I gig clubs with it and it sounds Glorious with JAN Phillips 6V6 tubes in it. Slight overdrive, clean when you back off the volume, great visceral lead tone with a Super Overdrive or Marshall Guv'nor in front ! I wouldn't part with mine, or change the tubes to EL34 !
Dunno, it hasn't arrived yet, it's listed as having no valves and with broken transformers, so I'm assuming the output got shorted or something and he couldn't be bothered to fix it so just took the valves out and sold it. I found a web resource that lists which (Hammond model) transformers to use for different valve amp applications:-
So if it could be done, I would be loading in a[FONT=Arial, Helvetica, sans-serif] 1645,[/FONT] [FONT=Arial, Helvetica, sans-serif]272FX and pair of EL34s for 30W or a [/FONT][FONT=Arial, Helvetica, sans-serif]1650E[/FONT], [FONT=Arial, Helvetica, sans-serif]270DX with 6V6s for 15W. I dunno how it can be rated at 30W though with 2x6V6, because they are rated at 15W for one pair.
There we go! It IS possible given the right transformers.
It would have been infinitely useful to include this info in the first post. That way TGP's wouldn't have been floundering around for 2 days making speculations on top of other speculations
So no circuit changes then? (Besides bias obviously but that's not really a circuit "change".)
Bias will be similar.
It's impossible to comment on circuit changes without a schematic. It should probably at least "function" with no changes.
Seems to work on this amp as well,
Note where it says FOUR 6V6's or TWO EL34's. Four 6V6's will have approximately the same primary impedance needs as two EL34's (or close enough for rock & roll). And 6V6's have approximately the same bias voltage needs as EL34's, so an amp designed for one will typically be able to be biased properly for the other.
Still doesn't mean they are directly interchangeable.
I would strongly recommend you get an amp tech involved to save yourself some grief . Is it possable?....probably with someone knowing what they are doing .