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Well a few years ago I bought my son a Scott 299D which uses 7591s. Since then a couple of the 7591's have bit the dust. I bought one of the EH 7591s to try it out, but it barely fits next to the output transformers and forget about putting the wood case back on - it sticks up way too high. Anyone know if EH or another manufacturer plans to reduce the size of these things? Looking at the tube it seems to me that the envelope is much larger than it has to be -- why? In the mean time, any recomendations on how to retube this thing? I really don't want to invest hundreds in NOS and I'm not sure I want to risk used ones.
Thanks, Steve
While the fit is tighter than the original, smaller version, they still clear the transformers by a comfortable margin.As far as height yes, forget the cabinet. But in the interest of a cooler running amp, you should forget the cabinet anyway!
~~b
You are "fighting" simultaneously on 2 fronts: electrical and mechanical.The 7591, the 7868, and the 6GM5 are electrical equivalents that are based respectively: Octal, Novar, and Noval (9 pin miniature). NOS of all 3 types is scarce and expensive. Of the 3, the 6GM5 is the most reasonably priced.
The "affordable" EH 7591 is a bad mechanical fit for your equipment. The EH 7591 uses the bottle and plate structure from the Russian 5881. The economies of scale are passed along to the consumer in the price, but the tubes are too big, physically, for many units.
IMO, you have 2 routes to follow. UOS 7591s from a reputable dealer will allow you to put the unit back into service quickly. AA sponsor Jim McShane (http://pages.prodigy.net/jimmcshane/), who I know from personal experience to be a GENTLEMAN, shows 2 strong UOS 7591s on his web site. The 2nd route is to convert the amp to use 6GM5s and stockpile 6GM5s for the future. AA sponsor Bottlehead Corp. (http://www.bottlehead.com/) offers a product called the Hole Shrinker that is designed to make conversion from Octal to Noval easy. Radio Electric Supply (RES) (http://www.vacuumtubes.net/page/indexc.html) and Tube World (http://www.tubeworld.com/) have listings for 6GM5s, with RES showing the lower price. Check out other NOS tube sellers for 6GM5 stock while you are at it.
BTW, you might combine the 2 ideas I gave above and get used 7591s for the short run while you accumulate your 6GM5 conversion materials. Sell all of your used 7591s after you convert to 6GM5s.
Eli D.
my 299 from 1960 ucalls for 7189s you sure you have the right tubes in there?
Your amp is not the 'C' model!
Oops again, I meant the 'D' model.
sorry youre right. it just says model 299. sorry for the inaccurate advice
No need to. I blame it on my typos. :-)
The EH7591s I've seen appeared to be the same size as NOS; I didn't have an NOS for comparison, but it LOOKED the same size. I've heard (this is not necessarily true) that until a couple years ago EH or Sovtek repinned a 5881 and called it a 7591. I read that on the Asylum and cannot verify. If true, perhaps that is what you have. Chris
The EH7591A definitely has dimensional differences to the original versions. The original design has the envelope length measured from the base of the seated tube at 2 5/8" with the envelope diameter being 1 1/16". The EH version is 3 5/16" and 1 3/8" respectively. I am currently evaluating a set I purchased recently for use in my Ampeg Gemini 1 guitar amp. In this case the dimensional difference is not a problem. I will have a more thorough evaluation of their sonics posted probably next week. I have about 50 hours on them so far and I want to adjust the biasing and note the sonic changes with the different bias settings. As for gear that cannot use the enlarged envelope, your choices are buying NOS at high prices, modify the amp to use 7355's or 6V6's. I have also heard of using 6GM5's with a socket adapter that AES (and others) sell but it could also cause dimensional problems for some gear. It is too bad the EH could not manufacture the 7591A in the same size envelope. It would have made a lot more people happy
"Nothing quite like high voltage DC to sharpen the mind and body!"
SG,Look at the guts of the EH 7591A and the NOS Westinghouse. The EH 7591A probably couldn't fit into the old straight side glass tube.
There's quite a bit of difference in the internal construction of the two tubes.
The new EH 7591A guts has very similar dimensions to the old US made 6L6GC. Even the glass envelopes are about the same size. Interesting, isn't it?
AFAIK, the EH 7591 is electrically identical to NOS, but New Sensor is using the same bottle and plate structure that go into the Russian 5881.
Eli D.
Eli,I wonder if it's the Class "A" setup that seems to bring out the difference. Maybe the EH 7591A would be fine, in an AB1, fixed biased amp.
But, that darn EH 7591A sounds like a lower powered 6L6GC (which is not bad, just different) in my amp. And the NOS 7591A, has this warmth to it---that rebiasing and twisting guitar volume and tone controls & changing pickup positions just can't squeeze out of the EH tubes.
I don't have a tube burner---but, I'm going to give those EH a good few hundred hours of use, before making my final judgement.
steve
Well the one I have is about the size of a 5881, but it was supposed to be the new EH from Triode Electronics. I saw on their web site that they list the size of the tube, maybe I'll measure the one I bought and make sure it is correct. OTOH, I am pretty sure I've seen others comment on the larger physical size. The original 7591s are about the size of a 6V6 or 6BL7.
Steve
Economics! In order to keep the cost down, the EH 7591 was designed to use the exisiting glass envelop from the 5851. JC from Sovtek mentioned this to me several months ago. Anyone used the new KT88EH?
Oops, it is the 5881.
Seems like a stupid decision since much vintage equipment that uses this tube was designed around the compact size of it.
Steve
New tooling would probably drive the cost way up than the current affordable price. Maybe the tube was designed more for the guitar community than the audio folks. In this case, we can't have the pie and eat it too. :-(
DJ,The same problem exist with those of us, in the guitar amp world. The EH 7591A can't be used in some Ampeg units (the amp company that used the 7591A, for many of their amps). Any combo amp using Jensen or Weber Alnico---the EH 7591A won't fit.
And with heavy ceramic magnet speakers--like Celestion Vintage 30---the EH tube barely fit and there seems to be EMF coupling between the magnet and one tube. A real pulsing glow, that is a function of the speed and depth of the tremolo circuit.
As I posted before, I felt that the tone was quite a bit different than NOS Westinghouse or Sylvania. This pseudo-test was done using an Ampeg guitar amp. I had to remove the amp from the cabinet to do the test---as the coupling was very bad, indeed.
Once the tubes were moved away from the speaker, there was no more pulsing. I also need to bias the EH 7591A higher (Class "A" amp) to get some of the midrange out of the tube. This is the primary weakness of the EH versus NOS stuff. The NOS 7591A just sounds so much different in the midrange---it's almost as if the pickup on my guitar was changed or removed---so that I could no longer get midrange tones.
EH's bass and treble as good as the NOS. But, the Ampeg's midrange is what gives it the unique non-Fender or non-Marshall character.
It would be interesting to see a printout of the electrical characteristic of both the EH 7591A and the Westinghouse 7591A. Because unless that EH needs a ton of break-in time, it sounds like a different tube, to me.
BTW---The EH 7591A is almost 1/2-inch taller than a TungSol 5881. And the guts don't have the dimensions (the EH is bigger) of the Sovtek 5881 or TS 5881.I guess that you could have your amp re-wired to take a 5881 or 6V6GT. These would fit. And give the amp a totally different tone.
EH may have short changed themselves as well with the big glass envelop. I don't have the current EH7591 production to check for the internal structure vs. the yesteryear units. I picked up a quad of the KT88EH at the NYNoise and unfortunately the 7591 weren’t available at the gathering.
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