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Old 10th June 2008, 02:59 AM   #21
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Now, that's more like the green-print Sylvies I know!  You been scaring the life out of me, since the greenie Sylvania Ms have been my go-to tube for years, in several types.

Wonder why so many of your 6V6s got gassy.  That's not like the marque.

Aloha,

Poinz
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Old 10th June 2008, 03:04 AM   #22
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I pulled back the throttles a bit. I am now running 450 volts at about 70 mA. I get 7 watts out at 5% distortion. There is a pale glow when the amp is driven. When you remove the input the tube gets hot. It has been running like this for about 20 minutes.

Further testing will continue, but I need to remove the expensive OPT's so that I can attempt a total meltdown.
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Old 11th June 2008, 12:27 AM   #23
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Hey Tubelab, Have you ever performed your famous torture on 6LQ6 or 6GF7(A)? I have some of these on the way and am curious as to your experience with them.

mike
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Old 11th June 2008, 01:33 AM   #24
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I've heard some folks say that the Sylvanias which were the last of the production runs from about 1987 were not very good as far as vacuum etc. Could these be from right at the bitter end of production?

I've seen a few of those being tortured in an old Fender amp with a shorted cathode cap before. Also, I had a Deluxe Reverb that I repaired once that had run with little or no bias for so long that the bottom of the chassis was dark brown from the heat. I think those were Sylvanias in that amp, so when they are good they are good, when they are not, they aren't.

I have a few Sylvania 6V6's that I bought new in 1988 they have the green writing and I've used them in several amps with great results. I better give them a good looking over before I use them again!

Great test.
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Old 11th June 2008, 02:19 AM   #25
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Quote:
Hey Tubelab, Have you ever performed your famous torture on 6LQ6 or 6GF7(A)?
The 6LQ6's are far too expensive to "test" although I do have a large (hundreds) box full of odd voltage sweep tubes, and I just bought some ceramic 9 and 12 pin compactron sockets. There are some 6GF7's in the box. Some testing will occur, but I can't say when. This was just a spur of the moment thing that allowed me to get carried away. I keep dreaming up more stupid "tests".

OK, you want to really crank some tubes. You have a nearly bullet proof power supply, those pesky cathode resistors and capacitors have been eliminated, but there is still a pair of shiny blue Edcor OPT's hooked into the amp. I would really be bummed if I blew one of those up, so they have to go. So I must ask the really stupid question, has anybody tried using an old microwave oven transformer as an OPT? I feel another experiment coming on.

Quote:
I've heard some folks say that the Sylvanias which were the last of the production runs from about 1987 were not very good as far as vacuum etc. Could these be from right at the bitter end of production?
The date codes read 705 vertically and ABH horizontally. I don't know how to read these. These tubes came from a lot that I got at least 10 years ago. I don't remember the details, but I probably got them in exchange for helping to load / unload a truck or two. I got some wafer based 6SN7's at the same time. I kept a few and traded the rest away. The few that I still have work fine.

If I had to guess, I would think that there was some contamination or rust on the leads that go through the glass, thus creating the path for a slow leak. I believe that all of these tubes will eventually leak, since half of them have leaked already. I haven't tested them all but some work great, and some seem to work OK but the distortion is too high. I have found a couple that are showing some blue glow inside the plate even though the getter is shiny. I am going to run these hard and see if they get worse.

Just because mine are junk doesn't mean that yours, or anybody elses are bad. These are obviously from a bad batch that got shipped when it shouldn't. I have seen worse things happen when there is a deadline to meet.
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Old 11th June 2008, 02:38 AM   #26
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Yea,I'm thinking maybe it was a bad batch also.


Quote:
Originally posted by Poindexter
Now, that's more like the green-print Sylvies I know!  You been scaring the life out of me, since the greenie Sylvania Ms have been my go-to tube for years, in several types.

Wonder why so many of your 6V6s got gassy.  That's not like the marque.

Aloha,

Poinz

Same here,the green Sylvania's are good tubes,Usually.
I've been rocking them in my PP 6V6 amp for a few years,my favorite 6V6 so far!.
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Old 11th June 2008, 02:46 AM   #27
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Quote:
So I must ask the really stupid question, has anybody tried using an old microwave oven transformer as an OPT? I feel another experiment coming on.
OK, I just answered the stupid question. There is no UL tap, so I used triode mode. The thing does actually kind of work as an OPT. I think that the impedance match is wrong, but there is a bigger problem. The frequency response sucks. The 3 db points are 35 Hz on the low end (good) but only 140 Hz on the top end. I can get 4 watts in triode mode (550 volts remember) at 60 Hz but only 1/4 watt at 1 KHz.
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Old 11th June 2008, 12:10 PM   #28
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Quote:
Originally posted by tubelab.com


OK, I just answered the stupid question. There is no UL tap, so I used triode mode. The thing does actually kind of work as an OPT. I think that the impedance match is wrong, but there is a bigger problem. The frequency response sucks. The 3 db points are 35 Hz on the low end (good) but only 140 Hz on the top end. I can get 4 watts in triode mode (550 volts remember) at 60 Hz but only 1/4 watt at 1 KHz.
Well, if someone wanted to make a really small subwoofer amp, I guess it would work.

Wonder how big of a folded horn it would take to get enough output?



Regards,
Gordon.
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Old 11th June 2008, 10:02 PM   #29
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So I must ask the really stupid question, has anybody tried using an old microwave oven transformer as an OPT? I feel another experiment coming on.
Funny you should mention...

I have a big hurky microwave tranny sitting my work room that I have been dreaming of converting to a sub amp output transformer. Thinking that if I can figure out how to non-destructively open her up I could rewind one of the windings to get proper ratio. No need for fancy interleaving as nothing above about 200Hz is really of any consequences.

Might be a good use for those 6LQ6s.

mike
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Old 12th June 2008, 01:08 AM   #30
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Looks like you have a half decent power supply choke, but a really lousy output transformer.

I've got an old MOT that I ripped apart. I actually bothered to unwind the primary, leaving only the secondary on the core. I'm sure it's at least a couple Henries. The tough part is that one end of the secondary is tucked under the winding itself, and welded to the mounting plate. If I try to hook it up as is, I'll have 400 volts on the whole thing. I guess I could put the choke on the center tap, rather than in the more conventional location...

On a side note, has anyone ever tried use a 12AZ7 as the front tube on a Simple SE?
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