6L6s in old SVTs? I'm Confused.

[bryanf1999]

I have my eye on a'74 SVT Blackline.
It looks to be an original Blackline in good cosmetic shape as far as the photo shows. Regarding the sound I have yet to actually see it or play it; that would be next. But I have some homework to do first.

I was under the impression that the original SVTs had 6146 power tubes for the first year or so and then they were changed to 6550s. The fellow who owns this one tells me it has 6L6s in it. It's the first time I have heard of these being used in these fine old monsters. Can anyone give me the history on this? Would this have been a mod? Are they the same pin configuration as a 6550?

I read that 6550s have more punch and drive but the 6L6s are warmer and more even. The fact that 6550s are more durable also seems to be the prevailing thought based on my research. Could anyone confirm, deny or add to this for me?
What are the differences in the 2 tubes as far as availability and cost go?

I am on a quest to acquire my first vintage SVT and I want to be as informed as possible.

This is where you, my esteemed, long time TB partners in crime come in. What do you make of this?

Thanks, in advance, for your insight.

Bryan

[christw]

I think they were running 6550's by '74. The 6L6 would be alright so long as the amp were rebiased but it definitely won't have that standard SVT vibe. The biggest difference I find is that you lose the pillowy low end going from 6550 to 6L6. As far as cost, 6550 are significantly more expensive. I'd want a tech to check the amp for other mods before purchase though.

[will33]

They never came with 6L6's. I would have it looked at and get a price on reversing that mod and whatever else was done to it. Deduct that from the asking price.

[bgavin]

Many years ago, my Dad repaired my old Sears Silvertone guitar amp.
It had four 6L6 installed.
He said these tubes were good for an honest 15 watts, and would light a 15w bulb all the way up.
Dunno if these are good or bad in an SVT, but correct bias is mandatory.

[Fair Warning]

6L6 mods are common for V4B. This is the first I have heard of them in an SVT

[B-string]

6550's handle more plate voltage and have different screen voltage requirement than 6L6GC. 6550 was standard and other mods would most likely have been done to use the less capable tube.

[bgavin]

My daughter plays a 1985 JCM-800 that was found to have significant deviation from stock.
Dr. Rock here in Sacramento put it all back to the way Marshall designed it.
A number of changes were required.

It sounds like the OP's SVT has suffered some major tweaking.

[KramerBassFan]

It is possible he doesn't know what he is talking about tube wise?

Nothing against the seller, but who knows.

[Bassmec]

Originally Posted by KramerBassFan

It is possible he doesn't know what he is talking about tube wise?

Nothing against the seller, but who knows.

It would have to be a hell of a good set of 6l6gc to handle the plate volts of an SVT.
I would be very surprised if it did not have 6550's in it and I would be looking very closely for any mods that had been done to make this possible to immediately reverse all and any of them.

[BassmanPaul]

think about it.

If an SVT could run with readily available 6L6GCs, why would Ampeg go to the trouble of fitting transmitter tubes???

why would they then go to the 6550???

Re-biasing the amp will do nothing to reduce the plate and screen voltages to a level that the 6L6GC could safely operate with. If the seller is right and the amp has 6L6GCs I suspect that the power transformer has been changed out.

Yet another point: a pair of 6L6GCs will supply in the range of 50W. Six could give 150W. That could be pushed up to about 200-225W with special care being taken.

if the amp doesn't have 6146 or 6550 installed I wouldn't touch the amp with a ten foot pole.

[bryanf1999]

Thank you very much for all of the great feedback. I'm much better informed now!
I will definitely be following up with the seller. I suspect it could be that his English is not great. If that is the case maybe they are 6550s after all. Who knows?

Anyone else feel free to toss your 2 cents in. JimmyM?

'Much Appreciated

[two fingers]

If it does had 6l6s in it, I probably wouldn't pull the trigger. It has either been heavily modded or the guy just switched out the tube sockets and has probably fried a set of tubes every 20 minutes. Either way, it would take some research and tech time to get it back stock, which IMO is where you want an SVT. Why bother getting a vintage SVT if it doesn't sound like a vintage SVT?

All this being said, my gut tells me the guy just doesn't know what he's talking about. He has probably heard the term "6L6" thrown about once before with regards to tube amps, and now he thinks that if he says it has 6L6s it's more awesomer....er to potential buyers. I really hope I'm right on this one. Best of luck either way!

[BassNeo]

Is this the one you're referring to?

http://toronto.kijiji.ca/c-buy-and-s...AdIdZ433257289

[LowEZ]

Originally Posted by BassNeo

Is this the one you're referring to?

http://toronto.kijiji.ca/c-buy-and-s...AdIdZ433257289

Oh jeez, the photo is 9 years old!

[T-Bird]

Hi.

Originally Posted by BassmanPaul

Re-biasing the amp will do nothing to reduce the plate and screen voltages to a level that the 6L6GC could safely operate with. If the seller is right and the amp has 6L6GCs I suspect that the power transformer has been changed out.

^This.

There's several other possible ways to reduce the plate voltage to be able to run other tubes as well, but that's the "easiest" way to do it intelligently.

I could very well understand why someone would make such a mod though.
The available volume would stay the same by any practical means, but the tube breakup would happen at a lot lower SPL, not to mention the selection of readily available tubes in 6L6 & EL34 family.
In fact a mod I've been thinking about performing with my KT88 equipped Fame.

BUT... such a mod is relatively expensive to perform but it will definitely kill the resale value (the Fame has none, so no worries there ), unless the original PT comes with the deal. I would probably pay 1/2 of what an unmodded amp goes for.

Do keep in mind that depending of the legislation and/or insurance company policies, in the case of an accident they may want to know whether that said high voltage mod was performed by a licenced electrician.
Most certainly the case over here .

Regards
Sam

[bryanf1999]

Originally Posted by BassNeo

Is this the one you're referring to?

http://toronto.kijiji.ca/c-buy-and-s...AdIdZ433257289

The one and the same Neo.

[bryanf1999]

Originally Posted by LowEZ

Oh jeez, the photo is 9 years old!

That was my first hint things may be suspect. The tube thing seems to confirm it now...

[B-string]

So you now have a bargaining position if this is true. offer close to half, if they say it is still an SVT you can answer no it is not. It WAS an SVT and could cost close to 1000 to make it one again. Right now it is a case that has the name only?

[Downunderwonder]

The tone of the advert suggests no such negotiation will be entertained.

[B-string]

Then either they will or it is a definite pass.


AS pointed out earlier with 6L6's it is no longer a 300 watt amp.