Am I ok to run 6L6's in a 5E3 ?

[Rob Livesey]

Hi Chaps,

I want to know if I'm going to damage anything if I try this? It would be nice to get a little more headroom out of my 5E3 build. Transformers are Mission Amps supplied.

Cheers,
Rob.

[martin manning]

I'd just contact Bruce at Mission Amps. His transformers are spec'ed by him, so he will know.

[Rob Livesey]

I did, a while ago, no reply. I'll try him again.

Cheers.

[martin manning]

On the surface, ~2x the current re using 6V6's would seem a stretch unless the transformers are oversized. I see he sells a 5E3 "6L6 RC" upgrade for $10, but there are no details given. I say give it a shot. Bias them conservatively and monitor the temperature of the transformers closely. Maybe first see if it will idle for a half-hour or so without getting too hot. That will tell you if the filament winding is up to putting out the additional current.

[patrick620]

Running 6l6 the OT is going to want to see a different load is't it?

[Milkmansound]

just pop them in there - everyone else does

its a bit different sound but not much louder - you will notice the amp running much hotter though. Mine gets so hot with 6L6's that the power switch is too hot to touch to turn the thing off after an hour or so

I eventually went back to 6V6 but only because of the heat

[Zippy]

Hi Chaps,

I want to know if I'm going to damage anything if I try this? It would be nice to get a little more headroom out of my 5E3 build. Transformers are Mission Amps supplied.

Cheers,
Rob.

Check out the "Paul C mod" for 5E3 - available at Mission Amps as the Vol/Tone mod.

http://missionamps.com/5E3kit.shtml

FWIW, Bruce offers an upgrade OT trannie - your amp might have either the stock or 30W set.

http://missionamps.com/5E3kit.shtml

Best to continue to contact Bruce or perhaps post the trannie info here to see if someone recognizes the Heyboer codes.

[patrick620]

Hi Chaps,

I want to know if I'm going to damage anything if I try this? It would be nice to get a little more headroom out of my 5E3 build.
Rob.

You might save yourself some trouble and try a 12au7 tube in V1 with with the 6V6 tubes

[M Fowler]

Mission amps schematic shows 345v-0-345v 100mA PT.

I run 6L6's quite often just because.

Mark

[tubeswell]

The PT's HT winding ideally needs to be rated at 150mA minimum for 2 x 6L6s (including say 3 or 4 pre-amp tubes), and the filament draw for 1 x 6L6 is 900mA.

If the PTs other windings (heater and rectifier) aren't loaded to the max current-wise, then you can run the HT at a greater draw than the maximum rated load and it 'should' be ok. But I'm not saying it 'would' be okay.

[renshen1957]

Hi Chaps,

I want to know if I'm going to damage anything if I try this? It would be nice to get a little more headroom out of my 5E3 build. Transformers are Mission Amps supplied.

Cheers,
Rob.

Hi Rob,

The only thing to worry about is the 6V3 heater current, you will need about 2.4 amps for two 12A_7 and two 6L6 tubes. Most PT will handle 10% overage (because tubes vary). If memory serves me 5E3 PTs are rated at 2 amp for the 6V3 heaters, switching to 6L6s put a 20% overage. A quality transformer might handle it, but a PT is expensive repair. I know nothing of the transformers in the amp, so you will need some communication from Mission.

The potential for PT damage is inherent when continually running the PT at 120%. Overheating PT shortens the life expectancy. Most manufacturers use the schematic heater rating in their PT for the circuit, as money is a factor.

As to advice, if a client of mine called and said they wanted to run 20% more heater current through the PT for an amp I built for them, I would for liability insurance, law suit, and for my own peace of mine tell them the PT would have to be changed out. If the PT shorted or an unrelated electrical fire, etc, occurred I would be the one who'd catch hell from all sides.

When I built my first 5E3, I used a transformer with 6 amps of heater current, you could run EL34s, KT66s, 6L6GC, Chinese EL156, whatever would fit in the space.

To dispel a myth, even if you have sufficient heater current, you won't get double power out of the circuit (PT and OT will limit the power), just a different tone. The 6L6 doesn't break into distortion as easily as its derivative baby brother, so some perceive the tube as being louder or having more headroom.

I wouldn't go to the trouble of changing the OT, the 6L6 will have no problem with primary. Tubes are more flexible as to OT primary loads than is generally believed to a point. 10k could be used on 6L6 tubes, but your power out of the circuit will be reduced.

The original 5E3 had 12AY7 (EH makes these) tube in V1 which have less than half the amplification factor than 12AX7. So did most of the Tweed Amps when they switched to miniature tubes.

Another post recommended 12AU7. Try the tube in V1 and even V2. Other options are a 12AT7 or 5751 V2, or mixed in combinations. Tube rolling the preamp may be what you are looking for rather than new tubes in the Power amp. If clean is what you are looking for, 12AU7 in the PI might surprise, Garnet used this tube a lot, although he would use 100k resistors for the plate and cathode in the Cathodyne splitter (second half of V2).

Just my two Pence.

Best Regards,

Steve

[Rob Livesey]

Hi Chaps,

Thanks for all the great input and advice.

Re tubes, I'm currently running an EH12AY7 in v1 and an old RCA 12AX7 in v2, rectifier is NOS RCA 5Y3, outputs are NOS Brimar 6V6's. I'll try a lower gain tube in v2 as I have a few lying around.

A friend suggested that he liked a 5V4 in the rectifier, this ups the voltage a bit, does anyone have an opinion on that?

I got a reply straight back from Bruce this time, here it is:

"Not sure how reliable the high current idle condition would be with 6L6s and that biasing resistor.
However, I've used the exact same power transformer with a solid state version of a GZ34 rectifier and a Pro Reverb sized output tranny in a +25 watt fixed bias, Mission Crusader amp with a pair of 5881s.
Those amps have been running for at least 4 to 6 years now and I've had no failures of the transformers.

Bruce"

Cheers,
Rob.

[martin manning]

Hmmm... using a ss rectifier would relieve the PT of the 5Vx2A load for the vacuum rectifier's heater, and under those conditions at least, it can take the increased 6.3V heater current and 6L6-like HT current. It's still unclear that it can do both.

5V4 sounds like something you could try easily and see if the additional 30V or so DC is to your liking.

[Masco]

Hi Chaps,

Thanks for all the great input and advice.

Re tubes, I'm currently running an EH12AY7 in v1 and an old RCA 12AX7 in v2, rectifier is NOS RCA 5Y3, outputs are NOS Brimar 6V6's. I'll try a lower gain tube in v2 as I have a few lying around.

A friend suggested that he liked a 5V4 in the rectifier, this ups the voltage a bit, does anyone have an opinion on that?

I got a reply straight back from Bruce this time, here it is:

"Not sure how reliable the high current idle condition would be with 6L6s and that biasing resistor.
However, I've used the exact same power transformer with a solid state version of a GZ34 rectifier and a Pro Reverb sized output tranny in a +25 watt fixed bias, Mission Crusader amp with a pair of 5881s.
Those amps have been running for at least 4 to 6 years now and I've had no failures of the transformers.

Bruce"

Cheers,
Rob.

Where have you been hiding? Long time no hear Rob!

[Rob Livesey]

Where have you been hiding? Long time no hear Rob!

I'm always lurking !

I'm busy with work and bands and the amps have gone from collecting to just the ones I use and play out with.

I joined a quite busy band last year, The Stumble - http://www.thestumble.com and I spend a lot of my spare time travelling and playing. We've also just released a new album which has been a lot of work in the making, but very enjoyable too. We're really pleased with the end result and it seems so are a lot of other people. We're getting some radio play on Blues shows and we hope to have it played on national radio in the next few weeks on the Paul Jones Blues Show on BBC Radio 2. He has a copy and he's promised to listen to it, so fingers crossed.

Cheers,
Rob.