Reducing the output of my Laney Supergroup

Duppy03

Was thinking about swapping out the EL34's in my Laney Supergroup 60 in an attempt to reduce the output/volume. Maybe a pair of 6L6's or KT66's or 5881's.

Another suggestion that has been made, it to run it 8 Ohms into my 16 Ohm cab as this will reduce the output like a JTM45.

Am I completely barking up the wrong tree here?

ICBM

Yes.

It's in the wrong section for a start .

Changing the power valves for a different but similarly-rated type will make no difference to the output. The bias supply probably doesn't have enough voltage to operate 6L6-family valves correctly either. (Or not without modification.)

Running at the wrong impedance won't change the volume significantly, will change the tone, and will risk blowing the valves if you crank it. (Not a great risk, but more than running at the correct impedance.)

If you want to *significantly* reduce the volume:

http://www.tubeampdoctor.com/en/shop_TAD_Equipment_TAD_ToneBone/ToneBone_PENTODE_price_per_pair_converter_669?osCsid=7370d72a6bb28fd193dd14f1f6edc241

or

http://www.tubeampdoctor.com/en/shop_TAD_Equipment_TAD_ToneBone/ToneBone_TRIODE_price_per_pair_converter_668?osCsid=a44b77081dcbff712c16a3c8f5f474c9

(Triode converters will reduce the power further than pentode but also compress and smooth the tone more.)

Or, get an attenuator. The Marshall Powerbrake works very well with these old Laney amps and isn't difficult to find second hand.

Duppy03

Doh! Thanks for pointing that out, must have been the G&T's.

Cheers for al the info, will look into the options. The TAD stuff seems interesting.

samzadgan

i think you should give the amp to me as is...and buy a smaller 15w amps for yourself? deal??

jpfamps

The old Laney amps use ver-r-r-y high HT voltage be modern standards, typically 600 VDC on anode and screen.

This is technically OK for EL34s (maximum rating of 800VDC on the anode and 600VDC on the screens), but will reduce reliability especially with modern EL34s.

This voltage is definitely NOT OK for 6L6s, KT66s, or 5881s.

Nor would I try the TAD adapters for EL84s. Very few modern amps use such high voltages, so I would not be confident that these will work with your amp.

ICBM

Good point, I had forgotten that.

In that case the simplest answer (as usual) is an attenuator - unless perhaps you would want to modify the amp to substantially reduce the HT voltage.

ThePrettyDamned

That's an awesome amp.

Sorry, I can contribute no further, but ICBM and jpf normally cover the clever bits.

Duppy03

It is indeed an awesome amp. Looks like I need to revisit an attenuator.

jpfamps

To be honest I would be careful using an attenuator with this amp.

Driving the power amp into clipping increases the screen grid current massively. Not only does this amp have high screen voltage the screen grid resistors, which help to limit screen grid current, are relatively low for EL34s (stock value is 470 ohm), so using an attenuator with this amp should be done with caution.

It may be worth getting the screen grid resistors increased in valve (if they have been done already). I would suggest 1k5 as a minimum.

Duppy03

So when people put a pair of EL34's in their JTM45's does that keep the wattage to 30w or does it bump it up to 50w.

Does the valve rectification have much to do with the output power of an amp?

I've seen a few models of amp that allows you to select the type of rectification which in turn effects the output power,

jpfamps

Duppy03 said:

So when people put a pair of EL34's in their JTM45's does that keep the wattage to 30w or does it bump it up to 50w.

Does the valve rectification have much to do with the output power of an amp?

I've seen a few models of amp that allows you to select the type of rectification which in turn effects the output power,

Valve rectifier will reduce output power somewhat, depending both on the design of the amp and the type of rectifier used.

Putting EL34s in a JTM45 may not yield more power depending on the transformer loading. The JTM45 output transformer should give an 8k load to the valves, and hence the relatively low power. This loading is too high for optimum power for EL34s, although I don't know if Marshall use this loading in their reissues.

ICBM

Yes, fitting EL34s *and* a solid-state rectifier will push the power up a bit, but not to 50W because the transformer ratio is still different, as jpfamps said.

A valve rectifier directly changes the power of the amp because it reduces the available voltage to the power supply compared to a solid-state rectifier. Typically you lose about 10-20% depending on the type of rectifier valve and the current draw.

Valve type changes don't always affect the power (unless you're talking about something like 6L6s vs 6V6s), and if they do it can be up or down depending on the transformer ratio and the load impedance.

Fitting a valve rectifier to the Laney would be possible, but you'd need to punch the chassis for the extra valve socket and fit a small extra transformer for the filament supply, since the main transformer doesn't have one. But you can get about 90% of the 'tone' effect of a valve rectifier by fitting a big resistor in the HT supply, which doesn't involve either of these things. Unless you're comparing an existing amp with a valve rectifier to a modified one with a resistor, I doubt you'd really be able to tell the difference to be honest.

In fact, with the Laney you could deliberately use a resistor much larger than any normal rectifier valve resistance, so it could have more effect. That would both reduce the power and address the issues which jpfamps mentioned about them being hard on valves.