750 volts too much for 6l6GC plates? (need big PA advice)

[VA3UX]

This reminds me of 'active' days in ham radio. Years ago I built a 4-1000A RF linear amp but the audio section of the 4-1000A data sheet always caught my interest : two tubes in AB2 with 5 KV on the plates for 3900 watts output.
http://www.g8wrb.org/data/Eimac/4-1000A.pdf

[imaradiostar]

I appreciate all of the input. I haven't replied to the thread in a while so here is an update.

After much deliberation I've decided the church youth group is doing just fine. I am still going to build some amplifiers for myself. Of course these will lean toward guitar and bass use.

I have a dead hafler and a dead peavey cs 800 and an assortment of parts from other old biamp and sunn amps. I was thinking about investing in one of these to put the parts to good use:

600 watt mosfet amp

800 watt stereo mosfet amp

500 watt amplifier

lme49810 based amplifier

So yeah..a bunch of possibly sketchy stuff there. I have a bunch of dead solid state PA components (transformers, caps, heatsinks) left over from things I took apart when I was a teenager. I have little extra money to spend on a complete/functional solid state amp and these seem like a super inexpensive board like this might be a good solution.

Meanwhile- I think I'm gonna build some very high power tube amps for myself! My wife wants a "practice amp" for her bass. I think I might cut to the chase and build a 2x or 4x 6550 amp for her. If she thinks it's too big I'll buy her a carvin combo and keep the big one for myself.

jamie

[imaradiostar]

tubedepot.com has a bunch of big 4-400 tubes- even a pair of those should be able to make 1000 watts without too much trouble.

where do I buy transformers to go with them?

jamie

[J M Fahey]

750 volts too much for 6l6GC plates?

Yes.

The original plan was to use an Antek Inc pt (4t550) connected with 120v across the 240 windings

Wrong

This means buying 4 el34's and an antek PT- about $200

Weren't you "using what you have around"?
What's wrong about your "big pile of 6l6gc's" and your "silverface Twin PT"? which, by the way, complement perfectly each other.

I figured I could use the 6l6's .... and just pretend they're el34's
would they be happy with ..... 750 Vplate ....?

Are you kidding?

I know that Ampeg and others ran 600+ volts on 7027a's

7027, not 6L6GC

Another thought was to take a matched pair of solid state 60vct PT's and run them in series and reversed with a pair of doublers stacked so they'd make about 650 volts DC ....... 60vct secondaries used as primaries, in series so that I'd have two very stout 120vac primaries being used as secondaries- with doublers each tf would make around 325 volts which I could stack in series.

Why stop at that? Why don't just use 10 12VAC trannies, with their old secondaries in series to make a "super 120V" primary and their old primaries in series to feed a couple 813's with some 1600VDC?
Now that I'm at that, why don't also use some .1x1600V polyester caps for filtering? You would only need about 2000 of them.
C'mon, gimme a break!!
Won't even waste more time with your following posts, specially after the excellent advice you got, which you chose to ignore.
PS: I'd grab that CS400, either to run a lot of wedges or as a bass amp power unit.
You could warm the sound by building a cascode 807 or 6146 preamp.

[imaradiostar]

Aren't the 7027 just a 6L6GC with extra pin connections anyway? Yes. Feel free to argue but many people using 6l6's in 7027 holes will disagree and then laugh all the way to the bank while you look for "true" 7027's.

And you're right, buying a pre-existing amp for wedges is the best solution. I wanted to try something different. I'm sorry if I didn't acknowledge but yes, people gave excellent advice. Unfortunately I'm back in school and don't have the income right now to just buy a power amp. If I did there are a few that are available locally as well.

6L6's will take 750 volts on the plates if screen current and bias levels are appropriate- of course not if screen voltages are too high! Will any old 6l6 do this? No. I thought I'd mention the 807 (same guts IIRC) lists 750 plate and 300 screen for RF AB1 use so it's doable.

This was an exercise in trying to use up some parts- at the time I was going to build with what I had laying around. The need has passed so one day when I'm in the mood I'll build something appropriate. I realize this post was somewhat ridiculous but that's why I asked- i figured there are a lot of outside the box thinkers here.

If I wanted 40-45 watts per channel I'd have used the twin PT. I wanted more like 80-100 per channel and I have two sets of rather large output transformers that should support that output level without too much trouble. EL34's with 800 on the plates and 400 on the screens would have been a perfect match. I'm not so naive as to actually think a 6L6 could drop right in and play nice!

As for the ebay power amp board options- once again, trying to use up parts and I have little budget but lots of time. Your comment about the multiple transformers, while intended to be funny isn't so far off from functional- there are plenty of applications where stacked secondaries are used to achieve a B+ voltage and retain lower voltage taps for screens and preamps. If I had some big transmitting tubes around I'd use them too.

I consider this horse beaten to death- unless anyone has good or bad things to say about the cheap-o ebay power amps.

Thanks to all who offered advice- I'm sorry I didn't acknowledge it. You're right- buying a used PA amp is the way to go.

jamie

[ThermionicScott]

Some of the later 6L6GC-equipped Music Man amplifiers put 700V on the plates, 350V on the screens. The screen voltage was taken from between the 150K bleeder resistors in the stacked filter capacitors.

Say you're looking at a graph of tube characteristics, and you draw a load-line from a spot (at cutoff) where the plate and screen voltage are equal (like in most BF/SF Fenders) to the "knee" of the curves. If you then double the plate voltage (keeping the screen voltage the same), you'll need to double the load impedance in order to intersect the knee. Dig up the 6L6GC chart where it shows screen voltages of 400, 350, 300, etc, and you'll have everything you need to figure out the ideal load.

Hope this helps.
- Scott