Converting a 6L6 amp to a 6V6 amp??

bandmaster188

Was just wondering if this is possible and how much work would be involved. I have two Silver face bandmaster reverbs both of which I really like. But i've been wondering if one of them could be converted to run on 6v6's to reduce the power for earlier breakup. If so how much power reduction would there be from the 45 watts stated? Would it just be a case of rebiasing the amp or would cap and resistor values need to be altered? And what tonal effects would this have on the amp?

ESchap

Looks like you can, from various threads on amp forums, but you're at the top end of even the JJ 6V6S capabilities and it will be a lottery with NOS valves.  Seems the key thing is that you make sure the screen voltage is at least 10v below the Anode, you'll need to change the resistors for that from 470 possibly to 1k or even 1k5 to be safe, they'll also need to be 5 watt or thereabouts.   Then need to re-bias it down to about 12 watts per output tube.  Not sure if you'll notice a huge volume drop but it will sound different for sure, more compressed?

 

 

bandmaster188

Yep. I was thinking this might be an expensive mod. :-O

ecc83

Well the Princeton B1270 runs 6V6 at 420V  which is pretty hot for the wee valve!

You should be able to get the bias right but I shall leave things to the Top Chaps. 

Dave.

ICBM

With 6V6s you would need to change the speaker impedance as well. You also won't get that much volume reduction - about 3dB - and it will change the tone... even if it works reliably.

Buy an attenuator. Earlier breakup at any volume below what you have now, no mod to the amp.

knuckleberryfinn

Or you could fit a PPIMV, which is an easy, cheap and reversible mod (as long as you mount the pot where the speaker extension jack is).

jpfamps

You can get away with running 6V6s higher than the "recommended" HT; the Jim Kelly amps used around 470 VDC.

If the HT is around the 450 mark (a typical value for the Bandmaster) then JJ 6V6s will be OK. I wouldn't risk it with any higher HT though.

Increasing the screen grid resistors to 1k5 will improve reliability.

6V6s ideally need a higher loading than 6L6s. A Bandmaster has a 4 ohm output, so plugging an 8 ohm cab into the amp will give a better loading.

You may need to adjust the bias supply to get into the correct range if you go for this mod.

bandmaster188

cheers for the input fella's. some food for thought there.

these are great amps and they have a lovely rich, warm tone and they drive really nicely when cranked, but to get them to that level usually results in bleeding ears! i get great results though using a couple of different drive pedals so i will probably leave well alone rather than risk frying their insides. it would be nice to hear that natural distortion at pub gig levels though. and don't say sell one and get a deluxe reverb. maybe i should. NO!

ICBM

bandmaster188 said:

these are great amps and they have a lovely rich, warm tone and they drive really nicely when cranked, but to get them to that level usually results in bleeding ears! i get great results though using a couple of different drive pedals so i will probably leave well alone rather than risk frying their insides. it would be nice to hear that natural distortion at pub gig levels though. and don't say sell one and get a deluxe reverb. maybe i should. NO!

Attenuator.

(For a recommendation, the Hotplate works really well with Fender BF/SF-tye amps and is available in a 4-ohm model. Discontinued now I think, but not rare.)

bandmaster188

Just been having a look on ebay and this http://www.ebay.co.uk/itm/BRAND-NEW-Dr-Z-Brake-Lite-Amp-Attenuator-DR-Z-FREE-USA-SHIPPING-/271435807928?pt=LH_DefaultDomain_0&hash=item3f32d5bcb8 looks like it'll do the job. It's a bit pricey but I like the way it can be mounted inside the amp or cab.

ICBM

Just my personal opinion, but I think the Brake Lite is massively overpriced, quite crude and not even particularly well-built. I don't think it sounds very good either.

Regardless of the claim that it will take any amp of up to 45W, I doubt that too having seen the internal components. (Bearing in mind that a cranked 45W amp can put out potentially up to 90W.)

For that kind of money you can get a much better attenuator, especially if you go second hand - you might even get a Hotplate for that, which will unquestionably take the power and will sound really good with your amp.

crunchman

I had good results with a Fender HRD and a Weber Minimass, although I wasn't cranking the amp wide open.  It's rated at 50W but I'm not sure I'd want to risk cranking a 45W amp into it.

The higher powered Mass might be worth a look.

bandmaster188

Are there any other brand attenuators that are worth looking at so I've got a few options?

ecc83

bandmaster188 said:

Are there any other brand attenuators that are worth looking at so I've got a few options?

Motherloads are the dog's bllx if you have the wonga.

Dave.

ICBM

ecc83 said:

Motherloads are the dog's bllx if you have the wonga.

I have one I'm selling, too…

But it's much more expensive than a second-hand Hotplate, and I'm not convinced it sounds any better as a straight attenuator, for this sort of amp. The main purpose of it is the emulated output, which is second to none.

The Marshall Powerbrake is good, but less so for this type of amp and only has 8 and 16-ohm settings.

The Original Dr.Z Airbrake is good too, despite my earlier comment about the Brake Lite.

I would avoid the "Ultimate Attenuator" - it's actually a solid state re-amp system rather than an attenuator, and the one I repaired some time ago was poorly made. It didn't sound that great either - not terrible, but nothing as special as the hype would imply. And is expensive.

I didn't think much of the MiniMass I tried for either quality or sound, but the larger Webers look better made and do have a good reputation.

Not familiar with any of the newer ones on the market.