7355 Power Tube Help!

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7355 Power Tube Help!

Postby hilldweller » Thu Feb 07, 2008 7:14 pm

It seems that this tube is extinct. I see no sub for it in the tube manual. A few years back, I could get these from AES. They no longer have them. I have a really nice HK TA-5000 reciever that needs these tubes. Can anyone help?, Can I modify to use a different tube? I am still learning so I appreciate all of your help. THANKS!
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Postby erichayes » Thu Feb 07, 2008 9:08 pm

The 7591 is close enough to the 7355 to be dropped in PROVIDED pins 4 on the sockets are not being used as tie points. If any or all are, the wires/components will have to be removed from the socket and relocated to single lug tie strips or turret posts. You might have to fiddle with the bias--it's been over 20 years since I modded one, and it was an A500, rather than a TA5000 (same electrically, different layout).

Since H-K was the only major manufacturer to use 7355s, its resurrection is highly unlikely. And now that both JJ and ElectroHarmonix are making 7591s (thank you, Ampeg), their prices will be getting more reasonable.
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Postby mesherm » Thu Feb 07, 2008 9:08 pm

Mike's N-1 Rule: When looking for N number of components to finish a job, you have a 95% chance of only finding N-1 of them.
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Postby EWBrown » Fri Feb 08, 2008 6:40 am

Some of these "new" 7591s are nothing more than 6L6s with a re-arranged pinout, Sovtek 7591XYZ being the main culprit, so I would also be suspicious of ElectroHarmonix, as well. The J/Js are alleged more like the real thing...

This from Gary Kaufman over at NNETG:

The 7591xyz is nothing but a sovtek 6L6 with a scrambled pinout to match the 7591. It biases up like a 6L6.

6GT5 has the same pinout as a 7868, but with a higher filament requirement and a bit different specs.

7868's and 6GM5's are less common than 7591's and don't sound any different imho.

Get some good ol' US made 7591's, make sure the bias is correct and the
coupling caps aren't leaky and enjoy.

EL34's in a 500C, yeow. That's some impressive filament draw!

- Gary


IIRC, 6JB5 is another interesting 12 pin compactron TV horiz tube, that has some useful audio applications...

(uppdate 2/22/08) I just looked up the 6BJ5 / 6JC5 / 6HE5 (Sylvania and Zenith) and they are basically slightly heftier 6V6s with a normal G1 bias voltage of -20 VDC. Also they have exactly identical characteristics to 6EZ5. Under the same "Class A" amp ratings, the 6V6 / 6V6GT has a G1 voltage of -12.5VDC.
But then free / cheap is always a good thing... Yellow_Light_Colorz_PDT_03


/ed B in NH
Last edited by EWBrown on Fri Feb 22, 2008 7:52 am, edited 2 times in total.
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Postby lynxx » Fri Feb 08, 2008 7:58 am

Also check this site. He doesn't have it listed in his price list but he has been quite helpful on my questions.
http://www.radiotubesupply.com/
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Postby erichayes » Fri Feb 08, 2008 1:52 pm

New Sensor's Alan Otto told me years ago that the 7591XYZ was nothing more than a reconfigured 6L6, which is why it needs a different resistor for cathode bias operation. When they came out with the 7591EH, I called him to find out WTF. He said the 'EH is a sure 'nuff 7591, painstakingly reverse engineered from the GE original.

When JJ came out with their 7591, I asked Bob Pletka of Eurotubes the same question. I got essentially the same answer.

I've used both in Fisher 500/800 series, and Sherwood S-7000 receivers with excellent results. If I could get a NOS 7591 without having to refinance my house, I'd throw it up against the new ones on the 570 to see how close they really are, electrically. Physically, both the JJ and EH are larger than the NOS tubes--which poses problems for those folks who have wood cases on their receivers.
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Postby EWBrown » Fri Feb 08, 2008 1:55 pm

Gary told me that several years ago he had a receiver with four very "tired" Radio Shack "lifetime" 7951s in it, so he took the tubes to the local Rat Shack, and yes, indeed, they honored the guuarantee, it turns out that they have an arrangement with AES, to be their supplier.

He also said the four replacement NOS 7951s were the most mismatched set of four that he'd ever seen :o Yellow_Light_Colorz_PDT_02

/ed B in NH
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Postby Tom Bavis » Mon Feb 11, 2008 9:16 am

The EH and JJ are electrically 7591s, which will require rebiasing to replace 7355s. The Sovtek 7591XYZ has two advantages over either... (1) it's electrically a 6L6 - very close to the 7355 and (2) they're cheap, cheap, cheap. Only disadvantage is size - they're bigger than the 7355 (as is the EH 7591)
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Postby erichayes » Tue Feb 12, 2008 4:13 pm

Found this site while looking for 6C10s. He has 7355s listed for $25.00 ea.


http://www.hamtubes.com/tubes/
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Postby EWBrown » Mon Feb 16, 2009 10:58 am

Just picked up a Harmon-Kardon A50K (A500 which was a kit) 7355 integrated amp, for dirt cheap $) . Works and sounds excellent, gave it a four hour test run yesterday. Maybe there is one good side to the current economic mess, after all. :/

I figure that someday the existing 7355s will go TU, and then I'll have to re-configure it for other output tubes.

The A500 uses a weird mix of catrhode and fixed bias for the 7355s.

Basically all four 7355 cathodes are tied together, and it uses three 12AX7 filaments connected in series, with a series connected 330 and 47 ohm resistor connected parallel across them.

The cathode voltage indicated on the schematic is 29V (which seems low for 37.8V worth of filaments. The 47 ohm resistor is connected to ground, and the junction between that and the 330 ohms resistor is then fed to the "cold" end of the 7355 grid resistors, thereby impressing about +3.5VDC on the grids, which are then 25.5V negative in relation to the cathodes. This may also offer a bit of DC feedback in order to partially regulate the combined cathode currents. Whatever it does, it seems to work well... FWIW, the three preamp tubes with the 29VDC filaments take a LONG time to warm up, as compared to the "downstream" AC-filament drivers and 7355s.

Power supply is the usual SS rectifier full wave voltage doubling scheme, main B+ is 370VDC, then various lower voltages are R/C tapped off as needed for teh preamp / driver / PI stages.

This amp was cheap enough so I wouldn't feel bad about turning it into a "parts donor" if it wasn't up to snuff, or if the 7355s die off and are too expensive to replace. Cosmetics are a tad "rough" with some scuffs and scratches on the front panel, but overall it is very clean and not too much rust / corrosion, jus a few specks on the top of the chassis.

. It's a "keeper". [:)

Looks like pin 4 and 1 of all of the 7355s were used as tie points =:o :'(


/ed B
Last edited by EWBrown on Wed Jan 05, 2011 9:11 pm, edited 1 time in total.
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Postby CharleyW » Sun Feb 22, 2009 9:23 am

If you turn it into a parts donor, and if you have the all the front panel knobs, I would love to purchase the knobs.
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Postby TerrySmith » Fri Apr 24, 2009 1:02 pm

I was digging through some long forgotten about boxes and found a Bogen RPF-60 receiver, and yep, it's got 7355's. (brb) Two test good, one weak, and one looks like it went through a nuclear test, the entire plate structure is completely distorted, and it still tests good, go figure.

This receiver will be a guinea pig for rebuilding can caps. I cut one open, they really stink! (sick)

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Postby EWBrown » Fri Apr 24, 2009 6:14 pm

That warped 7355 must have served some hard time in one of Ozzie Ozbourne's guitar amps... =:o

IIRC Bogen also used 6AV5GAs in some of their designs, and really cranked the s**t out of the B+, but ran the screen at 250VDC regulated with a 6CG7 circuit.

The Karmon Hardon 500 is still playing very nicely, its 7355s are still hanging in there...


OK, I'll admit that I'm an old phart, so what exactly does (brb) mean?

(duuuhhh, howzabout "be right back" :$ (???) :/

I could think up some PG-13, M and even X rated meanings, but then I can be somewhat "twisted" after a few (wine) (b) (d) (cig) adult beverages on a nice warm Friday evening...

/ed B
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