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Discussion in 'Amps and Cabs [BG]' started by newbold, Feb 21, 2016.
Is there any real reason anyone would feel the need to set a V4B up with 6550s or KT88's??
Are we talking about the original ones or the reissues?
The originals supposedly could put out more power with 6550s/KT88s while the reissues can not.
Mine is an original.
You can get a slight bump in power, but 50/50 chance of your power transformer not being able to handle the increased heater current. The 6550/KT88 tubes draw up to an additional 4 amps in heater current for the quad. You should change screen resistors and of course the bias will need to be reset (resistor swap in the bias circuit). You can also run 6L6GC/KT66 with just a bias adjustment. The one I had ran a touch over 120 watts output with 6550/KT88. 6550 and KT88 is basically the same application, just like 6L6GC and KT66. The 7027A's were a higher "grade" (supposedly) 6L6GC with doubled connection points.
Then it should be good to run KT88/6550s. Just follow @B-string's advice. He knows his stuff
Tonally/responsively...is it a case of having more clean or is it merely a power deal?
I found the very low end a little deeper at the expense of sounding fuller on the low end. Slight increase in power before the start of distortion. Example Before (my ears are sensitive to artifacts) with 7027A's at just a hair over 11:00 with the volumes was max before I could detect distortion, with 6550's close to 12:00.
Ampeg used to sell a performance kit for the V4B. It was simply a set of 6550A tubes and a set of tube retainers.. The power supply was designed to be able to cope with the higher current draw of these tubes. They claimed that this would increase the output to 130W.
Details in the portaflex wiki Sales Literature and Advertisements | TalkBass.com. See page three of the brochure, options.
I've had two V4s, both early 70s era. The first was "converted" to 6550s before I got it and I had my tech at the time make sure it was running right, set up a bias adjust, etc, to get things in optimal condition. On the amp I currently have I'm still running 7027As but I've done the coupling cap mods (C3 and C7) as well as replaced other parts to keep it in "top" shape (since I was doing the work and not paying extra for it). Between the two I'd say your assessment is on point. More low end roundness with the 6550s, more of a clean/even response with the 7027A amp. Maybe a tad cleaner at higher volumes on the 6550s. The 6550 amp ran much hotter. I wouldn't bother with converting another one having played both, but I'm also in the fortunate position of also having an SVT for higher volume gigs.
I converted mine as 7027A's were getting expensive and harder to find. I was buying direct from Svetlana with a quad of 6550C winged C's for $44.00 + shipping. 6L6gc(family) winged C's were a tad more. Actually the first set was 6550B's that oscillated, exchanged and the B's were good. The C's came out and the amp left me with them in place still in prime condition after a few years of service.
Normally a V4B with 7027A's runs hot. With 6550A's it runs even hotter. Adding a fan helps.
Yes sir, it help a lot .
I bought a V4B used on Craigslist a few years ago as "broken" and brought it into Central Jersey Music service (known for their Ampeg knowledge) for repair. The only real problem with it turned out to be a short in one of the JJ 7027s. The tech remarked that he had been dissatisfied with the quality of newly made 7027s (JJs) and recommended switching to 6550s.
I keep waiting to hear a good report on the JJ's, but I am breathing in the meantime.
Many J/J tubes are as good as are made today, but not the 7027A, and unfortunately, tubes today aren't as good as tubes were in days past.
The top types ARE getting better, though, but more esoteric ones seem to be getting the shaft. No doubt this is why Ampeg went with 6L6's for the new V4B.
My V4B has been modded to run on 6550s. It definitely runs hot, but I've not had any kind of performance issues in the past year of owning it. Couldn't say how it sounds compared to a 7027 model, but mine sounds great and performs wonderfully.
I, for one, hear a definite girthiness in the low end with KT88s in any amp that uses them. I don't have them in my V4b and I am very happy with the way it sounds, but I bet it would sound even better. They are expensive buggers, though, aren't they?
I don’t remember mine being THAT hot but;
I bought it used when I was 16 and sold it 35 years later with the original tubes
It had never been in the shop
I say the reliability of the stock design outweighs the very slight difference in performance
This is why I never bother with trying to top the original design. I figure if it could be topped, they'd already be doing it.