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7591A Power Tubes?


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7/30/2000 5:50 AM
Brett
7591A Power Tubes?
I have an old Sano amp with a pair of 7591A power tubes. Are the new Sovtek tubes any good? What other (cheaper?) tubes can I substitute them with? I know the pinout is unique. This is my first tube amp and I'm still learning. Thanks for any info.
 
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7/30/2000 6:25 AM
Peter S

The Sovtek "7591A" is not a 7591 type tube at all. They are Sovtek 6L6GC tubes. The Sovtek 6L6 is extremely poor substitute for a 7591. There really is NOT any cheap substitute readily available for 7591 type tubes. Forget the Sovteks. If you can't find 7591A's(highly likely), IMO, the best hing to do is rewire the tube sockets to accept 6L6GC type tubes and use the Phillips 6L6GC or 7581 tubes. These are still available in large quantities and would make the best affordable alternative to a 7591A. The Sovtek tubes won't come anywhere near close to the tone and clean sound of a 7591A. The Phillips 6L6GC/7581 does not sound like a 7591, but it is a good quality, reliable clean sounding tube with plenty of headroom and a big bottom end.  
 
Peter S
 
7/30/2000 6:35 PM
Dave M

Brett, I have seen another substitution for these in the Antique Electronic Supply catalog. They sell an adapter to run 6GM5 tubes in place of 7591A's. Supposedly the 6GM5's are electonically identical to 7591's but with a different pinout. The only problem is they add 1 1/4" to the height of the tube so you have to make sure there is enough room in the cabinet to hold these. You could also with a little work just change the sockets to accept the 6GM5 base. The 6GM5's sell for $22.70 at AES which is very reasonable for a NOS tube. I haven't tried 6GM5's yet though so I'm not sure if they sound identical to 7591A's but supposedly they do. If you end up trying these let me know how they sound.  
 
Dave M
 
7/30/2000 6:46 PM
Graywater

Folks,  
 
First, the 7591 is a very long-lived tube so make sure that you actually do need replace. Second, for lower power designs the 6V6 will retain more of the sound than will the 6L6. Third, the 6GM5 is much shorter than the 7591 so there won't be as much clearance problems with a adapter (and who made these adapters, mine are only about 1" high excluding the tube pins - easy to makle with an old octal tube base and a "Novar" tube socket). Last, the 7591, 7868, and 6GMA ARE the same tube - the assembled tube elements were just placed in different envelopes with different bases. Any discussion as to whether they are really the same tube is silly - get a couple of dead tubes, crackoff the envelope, and compare the guts.  
 
GW
 
7/30/2000 6:59 PM
Dave M

GW,  
Thanks for clearing that up. I've been considering buying some 6GM5's to replace a pair of 7591A's that are drawing about 50mA of current. BTW, you sell adapters?  
 
Dave M
 
7/31/2000 12:02 AM
Graywater

Dave,  
 
You wouldn't want to pay me for the time involved - but it's easier for me to just make something and just have it at hand when I want it than to buy it. Also,it lest me use up some of my material burden of spare parts I've got laying around. If you're really interested I could probably make up a "kit" for you from the parts bin with instructions for making your own for a reasonable price. Hey, what's AES, or whoever, getting for their adapters?  
 
Another Idea- since I use old octal tube bases to make various adapters (6SL& to 12A_7, etc) the source of the bases is broken/wornout/"worthless" tubes. Unfortunately, none of these is a tube with a wafer base - if I had a few of thesee (hmmm, wonder if there are any dead metal tubes in the attic?) I could probably reduce the adapter height another .375 inches or so.  
 
GW
 
7/31/2000 5:32 AM
Dave M

I think AES is getting around around 13 dollars for their adapters. I think I've seen some other places selling them but I can't remember where.  
I think I'll check and see if I have any old metal tubes with wafer bases in the tube caddy that my neighbor gave me. (He's a WWII vet so I'm sure there's a few metal tubes in there).  
 
Dave M
 

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