Ampeg V4
- Thread starter CJ
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ok here goes the print,
nice coil, hi-fi type, little bit of everything, bi-fi, reverse wind, 9 sections,
sec winds end up with 4 wires in parallel, this is done on other hi end transformers like the Peerless 16431 for the Heathkit W6M Williamson circuit, easier to wind than 1 big wire, lays down flat, less stress on the coil as winding tension is lowered, which is a plus when winding these old layered paper designs, leakage is also better with the quad secondaries,
we will re-wind with a bobbin as it is really an art to get a paper coil this big to come out nice and square, heck, just pulling a layered paper coil off the mandrel is tricky, best to used to wedges hooked to a spindle and take the wedges out of the coil from opposite sides,
this thing is loafing at 5 K Gauss, this steel could take 18 K Gauss, we used 190 V-rms in the B-max calcs, this core uses a 1.6 aspect ratio on stack height, so lots of iron,
Turns ratio is never a round number for pwr OPT's, engineers start with plate resistance and work their way down to turns ratio, so Z ratio might be a nice round number, but when you take the root, you get decimal places,
note the 2 ohm spec, kind of rare to see that, to get from 8 ohms to 4 ohms, divide by root 2, so 104/1,414=73.5, they use 78, but impedance changes a lot depending on frequency so it is a loose spec, thus the inexactness on sec turns,
nice coil, hi-fi type, little bit of everything, bi-fi, reverse wind, 9 sections,
sec winds end up with 4 wires in parallel, this is done on other hi end transformers like the Peerless 16431 for the Heathkit W6M Williamson circuit, easier to wind than 1 big wire, lays down flat, less stress on the coil as winding tension is lowered, which is a plus when winding these old layered paper designs, leakage is also better with the quad secondaries,
we will re-wind with a bobbin as it is really an art to get a paper coil this big to come out nice and square, heck, just pulling a layered paper coil off the mandrel is tricky, best to used to wedges hooked to a spindle and take the wedges out of the coil from opposite sides,
this thing is loafing at 5 K Gauss, this steel could take 18 K Gauss, we used 190 V-rms in the B-max calcs, this core uses a 1.6 aspect ratio on stack height, so lots of iron,
Turns ratio is never a round number for pwr OPT's, engineers start with plate resistance and work their way down to turns ratio, so Z ratio might be a nice round number, but when you take the root, you get decimal places,
note the 2 ohm spec, kind of rare to see that, to get from 8 ohms to 4 ohms, divide by root 2, so 104/1,414=73.5, they use 78, but impedance changes a lot depending on frequency so it is a loose spec, thus the inexactness on sec turns,
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there were only three sets of 2 x 2 so probably just a mistake,
there are some transformers with 3 or 4 Ni lams stuck in the middle of the stack, like the peerless 16431, don't know if they do anything or not, like Doc Hoyer says, just the engineer sticking a cherry on top of an ice cream Sunday,
there are some transformers with 3 or 4 Ni lams stuck in the middle of the stack, like the peerless 16431, don't know if they do anything or not, like Doc Hoyer says, just the engineer sticking a cherry on top of an ice cream Sunday,
OPT rewind complete-used 1 size bigger pri wire for better current capability,
bigger wire took more space so less turns, this thing had a ton of turns anyway, 2,000 on a huge core compared to 820 turns for a Marshall on a smaller core,
so we ended up with 1,550 turns instead of 2,000 and lower DCR, this comes out to a plate to plate load of about 1,800 for an 8 ohm load, but with lots of pri inductance, 764 H at 5 Hz,
we played games with the split pri turns to get a more balanced DCR, 420T for the inside wind and 355T for the outside wind, came out about better than the stock coil, 13.2 and 14.3 ohms for 27.5 which matches good 2with the 28 ohm middle pri wind, which is done in one section,
for a 16 ohm speaker, P-P load goes to 3.6 K Ohms. if somebody wants to plug in a 2-12 cab wired in series,
we used quad #26 like the Peerless 16431 instead of the bigger bi-fi wire of the stock Ampeg, the old wire that we saved was too bumpy to wind flat, would have run out of winding room,
turned out flat to 60KC, should sound good,
here is the coil ready to get hooked up>
bigger wire took more space so less turns, this thing had a ton of turns anyway, 2,000 on a huge core compared to 820 turns for a Marshall on a smaller core,
so we ended up with 1,550 turns instead of 2,000 and lower DCR, this comes out to a plate to plate load of about 1,800 for an 8 ohm load, but with lots of pri inductance, 764 H at 5 Hz,
we played games with the split pri turns to get a more balanced DCR, 420T for the inside wind and 355T for the outside wind, came out about better than the stock coil, 13.2 and 14.3 ohms for 27.5 which matches good 2with the 28 ohm middle pri wind, which is done in one section,
for a 16 ohm speaker, P-P load goes to 3.6 K Ohms. if somebody wants to plug in a 2-12 cab wired in series,
we used quad #26 like the Peerless 16431 instead of the bigger bi-fi wire of the stock Ampeg, the old wire that we saved was too bumpy to wind flat, would have run out of winding room,
turned out flat to 60KC, should sound good,
here is the coil ready to get hooked up>
Attachments
mjrippe said:I have heard a rumor about a repair shop here in Brooklyn with a stack of V4s. Seems the transformer goes and nobody wants to spend the $$$ to replace it. You wanna offer your services CJ?
Ha! I used to do solid state repair at that shop! When I left in '08 there were several shelves of beautiful v4's, v2's, vt-22's, vt-40's and the like - all had been left there by broke, broken hearted musicians, some even (ex)famous ones too…
I bet if you talked to the tech there, and could give them a good price - they would love to slap some new OPT's in them and put them on the floor - you can get a pretty penny for them these days...
thing is you used to be able to get these for nothing - they were the poor mans marshall. My first ever tube amp was a pristine 1968 V2 - it was like a classic car, heavy and lots of metal… over the years I bought several v4's and v4b's and eventually, and stupidly - sold that V2 to a studio in NC after coming home broke from a tour… its still there, and i still regret it to this day…
I have tried all the replacement tubes over the years, for a while there before JJ's came around there were no current production 7027's at all - you'd have to get them from ebay - but after a few mid show blow outs that option proved untenable. Then Sovtek started making them again and those were even less relaible than the old stock ones…
I have found the 6550's are the cleanest for sure, but since this amp has a pretty clean preamp section, to get any drive out of the 6550's you really have to crank it. for bass tho, or bands that use lots of fuzz/dirt pedals its 2nd to only the 7027.
e34l's or el34's sound ok for gtrs, but you loose a lot of the bottom and the high are more compressed then the 6550s or 7027's
6l6's wind up having a nice low mid but loose the brilliance in the highs…
To my ears, the 7027's, when stable, are the best hands down tho - its kind of the best of both worlds, low end galore, good definition in the high mids and they sound like nothing else when pushed hard.
I have 3 of these in the studio - a V4b with 7027's, a V4 with e34l's and a VT22 (V4/2x12" combo) with 6l6's and they all sound great for different things…
another + 1 for watching your fingers - these things do like to bite.
