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Custom V4B build from scratch...

#21
I just got my fourth V4 amp. This one is actually the first V4B that I've had, and it's the best sounding one yet.
I have looked into the idea of a 200 watt V4 head as well. The problem, as others have said is the transformers. It will take some serious iron to get 200 real watts of power with a V4 style head. I bought one the the new Traynor YBA 200 watt heads. Not even close to twice the power as a V4. The toroidal transformer they use will drive the tubes, but the iron in a conventional style transformer is where you get the stored power capability.

It would probably be a lot cheaper for you to buy two vintage V4 or V4B head and use both of them into two different cabinets. Actually it's already been done anyway, it's called an SVT! :hmm:
 
#22
kiljoy said:
Ok, after much deliberation with my tech guy we've decided to can the build from scratch idea. It seemed to be a cost effective idea in the outset but ended up calculating far too high in price. So... I've just bought myself an Ampeg V4BH which I know is nothing like the original V4B but it was all I could find in this half of the world.

I'm still considering the upgrade to KT88s and potentially a transformer upgrade too. Does anyone know of any preexisting modification to do this?
Click to expand...

If you are considering this "upgrade" you should supply a supplementary heater transformer of about 8-10A for the output tubes. The 6L6GC takes 0.9A at 6.3V for its heater. The KT88 and 6550 take 1.5-1.6A. Multiplied by the four tubes that's an extra 2.4A or so. Your power transformer will be at risk. Certainly its life will be shortened.

Paul
 
#23
I upgraded my Traynor to KT88's from the stock 6L6's. There was a difference, but it wasn't much. V4's do what they do very well. You are not going to squeeze much more out of them than the 100 watts. If there had been a way, I would still be playing the one I had in the 80's, instead of the 2000 watt Crown xti I use now for big gigs. For gigs that 100 watts will handle, the V4B is a great head. It is what it is...
 
#24
BassmanPaul said:
If you are considering this "upgrade" you should supply a supplementary heater transformer of about 8-10A for the output tubes. The 6L6GC takes 0.9A at 6.3V for its heater. The KT88 and 6550 take 1.5-1.6A. Multiplied by the four tubes that's an extra 2.4A or so. Your power transformer will be at risk. Certainly its life will be shortened.

Paul
Click to expand...

Just dropped the V4BH off at the tech again. He's had a separate transformer wound for the heaters on the 6550s and disengaged the heater feed to them from the main tranny, so that should free up a bit more current for the rest of the amp. I just played it at a gig on Sat night and although it sounded great I was running both the pre and power sections right on clipping point. It's currently rating at 81 watts clean, so right now I'd be happy with 120 to 150 watts. I should hear back from my tech in the next 2 days so I'll keep ya all informed.
 
#29
BassmanPaul said:
Just changing the output tubes will not give you more output power. To get anything more entails changing the transformers too.

Paul
Click to expand...

OK, update time. The amp rates at 101 watts clean (was 81w) and has a max clipping point of 163 watts (was 137w). Now that the extra filament transformer is performing the power tube heater feed the main PT is running cooler. I'm gonna give the amp a whirl this week at practice and we have a gig this Saturday.

The next test may be to install larger power caps for more headroom before clip.
 
#31
kiljoy said:
OK, update time. The amp rates at 101 watts clean (was 81w) and has a max clipping point of 163 watts (was 137w). Now that the extra filament transformer is performing the power tube heater feed the main PT is running cooler. I'm gonna give the amp a whirl this week at practice and we have a gig this Saturday.

The next test may be to install larger power caps for more headroom before clip.
Click to expand...

Because you removed the heater load from the power transformer the B+ voltage rose giving you a smidgen more power. The difference in use will be undetectable.

Paul
 
#32
Yeah, if you want to get 200W out of those four 6550/KT88, you'd better design your plate supply to give 700Vdc (like an SVT).

kiljoy said:
Hi guys, I'm about to embark on something of a mammoth task which is to build an early 70's style V4B from scratch with some power section modifications. I wanna keep the preamp as is but switch out the 7027s for KT88s and feed them the right power via a bigger power tranny to get the output to 200w. I have a good tech who will be doing the actual build as I'm fairly ******** with a soldering iron.

Are there any hints, tips or advice anyone can share?
Click to expand...
 
#34
BassmanPaul said:
Because you removed the heater load from the power transformer the B+ voltage rose giving you a smidgen more power. The difference in use will be undetectable.

Paul
Click to expand...

I tried the amp out last night at practice and it seems a touch louder with a little more bandwidth to the power section. I have some Svetlana 6550s in there at the mo that have already had some serious abuse, what would be a good choice for a new matched quad?
 

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