For all you hard core 6BQ6 cookers, the latest sale sheet from Leeds Radio, www.leedsradio.com , lists 15 NOS 6BQ6GTB for $1.00 per piece.
You have to call or email for the latest list.
No idea if they are the big ones or little ones.
Win W5JAG
edited to fix link.
You have to call or email for the latest list.
No idea if they are the big ones or little ones.
Win W5JAG
edited to fix link.
From my experience the 6BQ6GT, 6BQ6GTA and 6BQ6GTB are all the skinny ones (1.125 inch diameter). I have not seen any fat versions with these numbers on them. The "fat boys" are all labeled 6BQ6GA. I have found these in two diameters, 1.375 inch and 1.5 inch. The "fat boys" have bigger plates. The ones that are on sale at AES are all 6BQ6GTB. I asked for 6BQ6GA, and they said that they had none.
So far I have a 10% failure rate with the "sale" tubes. I decided to test some 6BQ6GA's that I got from Stan at the Tube Center. These were not on sale. I asked for some fat bottled 6BQ6's and I got 4 different kinds. In post #53 you can see the fattest one next to an ordinary 6BQ6GTB. So far it was the only one I tried.
I put these tubes into the same amp, under the same conditions as the 6EZ5's above. Short story, 10 tubes tested, 2 bad. One exhibits a runaway condition where the current will just take off when operated well within specifications. The getter on this tube is weak, you can see through it. The other lit up with a fireworks display when the power was applied. It arced at any voltage above 200 volts and glowed blue at 125 volts. It should be noted that BOTH of these tubes test good on my tube tester, yet both could cause serious amp damage. I can't blame Stan for these since a tube tester would not find either fault.
Be careful when experimenting with these old tubes, your amp could get zapped! So far all 4 bad tubes can be attributed to air intrusion. They were all sold as NOS, and none showed any signs of prior use.
In the 10 tubes that I got, there were 4 different constructions. Most were GE's. These have the same plate structure found in 6FW5's and some 6AV5's. They will take 25 to 30 watts without glow. There were 2 GE's with a smaller plate structure also found in 6AV5's, good for at least 20 watts. There was a Westinghouse labled 6CU6 with a stop sign logo made in Canada. Big fat plate, no glow at 35 watts. Also a Raytheon with a big fat plate, but it was one of the bad ones. The variability among these tubes is HUGE! The current varies from 30 mA to 200 mA with the same 30 volt bias setting. I had to readjust the bias for each tube.
What will these tubes do? It has been postulated that the 6BQ6 does not do well in SE, and up till now, I agreed with that. I had set the amp up for the 6EZ5 with the B+ at 300 volts resulting in 1.5 watts output. I dropped the 6BQ6GA into the same socket (adding the plate cap) and set the bias to the same 50 mA. The power output was over 3 watts with some distortion. Adjusting the bias to 60 mA killed the distortion and resulted in a power output of 4.0 to 5.0 watts in triode on every good tube. A little more voltage lowered the distortion some.
OK, this looks good, so what happens with the cheap tubes? I installed the previously seen "leaning tower of power" and one of its brothers. These came from AES for $0.98 each!. Yep, 5 watts in triode with a 325 volt supply! NO GLOW! Next, I hooked up some speakers and a CD player. Thes guys are absolutely the best sounding 98 cent output tube that I have ever heard. Well, they are the only 98 cent output tube that I have seen recently, but they do work good.
The details, B+ is 330 volts putting 325 volts across the tube. Idle current is set to 60 mA. It goes up to about 70 mA as clipping is approached. Power output is measured at 5.0 watts at 4.5% in one channel and 5.1 watts at 4.9% in the other channel. OPT's are Edcor CSXE 25-8-5K. Yes, this is 19.5 watts of combined dissipation, against an 11 or 12 watt spec. The little guys showed no glow after an hour of average music playing. I would run them a little cooler, but the "fat boys" should have no problem with this.
UL mode was not tried. This was just a tube testing experiment. I must tear this set up down to hook up the spud amp. I bought 50 6LR8's (also not on sale) for eventual use in spud kits. I must test them now based on the failure rates for these other tubes.
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tubelab.com said:
Well..., they didn't say how far "prior to shipment" they did the testing. For that matter, they don't say what constitutes a "test".
"Yep, fits in the socket. This one's good..."
BTW, I can appreciate your attitude about bedrest, man. I'm a poor "patient" myself, but do take care and mend well.
tubelab.com said:
Rust wait a sec, that had to of been there before it was assembled. Rust can't grow in a vacuum, it need oxygen to survive. Man talk about crappy quality control.
Not that it really matters but you could have some really small p[article flack off and get stuck some where important.
Maybe they test the tubes when they receive them to avoid storing bad ones. A slow leaker could then rust on the shelf. I had some tubes I got cheap that had a kink in their transfer curves. I found I could get rid of the kink by grossly overheating the filament for a few seconds. Probably was something absorbed on the cathode surface.
Where to get a 600 Ohm OT? Was that the Ebay 400W Plitron?
Don
Where to get a 600 Ohm OT? Was that the Ebay 400W Plitron?
Don
I looked at the GE data sheet and found the 6CU6 and the 6BQ6GTB/GA had the same specs, whereas the 6DQ6 looked very close but beefier.
I have a few of 6DQ6, 12DQ6, 6CU6, and 6BQ6GTB around, mostly used. The *DQ6's and a couple 6CU6 resemble the fat boys, and a few GE labeled both 6BQ6GTB/6CU6 on the boxes, but the old CBS 6CU6 are in fat boy size. However, the 12DQ6A is about 4X of the 6BQ6GTB, and the 6DQ6A is approx 6X at AES.
I have a few of 6DQ6, 12DQ6, 6CU6, and 6BQ6GTB around, mostly used. The *DQ6's and a couple 6CU6 resemble the fat boys, and a few GE labeled both 6BQ6GTB/6CU6 on the boxes, but the old CBS 6CU6 are in fat boy size. However, the 12DQ6A is about 4X of the 6BQ6GTB, and the 6DQ6A is approx 6X at AES.
SY said:
Buy. Damn, this is a bad time to be out of money.
I can't claim credit for this one, I was turned on to it by Greg the Geek and Erik deBest. It runs surprisingly well at lower currents (1-2mA) with CCS plate loading.
I was turned on by Greg the Geek and Morgan Jones, both making positive comments on the EC91 (MJ refers to it on pg596 of VA, third edition). 5,70 is still way more than I used to pay in the good old days when I paid 50 pence (that is, half a pound) a piece. Well, good old days...it was actually two years ago
Today I bought 40 pieces of the 12W6GT and 20 pieces of the 6KR8. The 12W6GT is recommended by John Atkinson for its linearity as triode, and was tested/approved by Lynn Olson as driver in his amps. Lynn's comments are that it 'sounds' close to old american 45, and better than newer Svetlana's 2A3. Dunno, but for 1 dollar a piece one can experiment a bit.
Erik
I got my 600 ohm SE OPT's used from another forum member. They are the same ones seen on Ebay under the Eastern Audio brand. They claim "50 watts" which might be true at 1KHz, but they are about a 10 watt OPT in the real world. I got them for experiments, which they are more than adequate for. They sounded pretty good in the hybrid experiments that I did as long as you don't turn things up too loud. James makes a 600 ohm OPT, but it is hard to find in the US, not cheap either.
The surplus Plitrons were huge 400 watt @20 Hz P-P OPT's. They are 1250 ohm CT made for a Marshall bass guitar amp. I have verified the upper 3db point as 71KHz at 150 watts. These were on Plitron's web site until they were mentioned here. Then they dissapeared in a week. They will be used to "test" some $2 tubes that should arrive tomorrow.
The 6DQ6 requires a lot more bias voltage. This is OK in fixed bias operation but makes for big, hot cathode resistors in cathode bias designs. Some of the "fat boy" 6BQ6's that I have found have the same plates as the 6DQ6. The best of both worlds. I have found 6CU6's in both sizes as well. I also have 6BQ6/6CU6 (GE and Raytheon) in both sizes. As soon as I find a reliable way of identifying the fat ones, I will let everyone know. I had planned a trip to the Tube Center's warehouse last week to have a look at a few zillion tubes, but cancer, a hamfest, and a tropical storm blew away my plans. My next oportunity may come in a few weeks.
That was my intention, but I have bought a whole bunch of $1 and $2 tubes.
The 6EY5/ 6EZ5 ($1 at vacuumtubes.net) is very similar to the 6W6 (except the rusty one).
The 6DG6 IS a 6W6. $1.70 from AES.
The 12L6 is similar to the 12W6, and may work better at low voltages. $1.13 at AES (limit 8 per customer).
But the 6BQ6GTB for $0.98 has to be the best dollar per clean watt deal of them all. Less than 25 cents per watt in triode! How many can I connect together to make an OTL?
Proof that too much talk about an uncommon tube will make the price rise. I may be partly to blame for the stupid prices on the 5842's now, since I said too much about those 5 or 6 years ago. I have talked to 3 large tube sellers about the 6BQ6's. All claim to have more of them than they could possibly sell. They were about as common as dirt when I was young, literally. I used to get them for free at the trash dump from old TV sets in the 1960's. Think of $0.98 as a storage fee for 50 years!
tubelab.com said:
I went out and checked my stash tonight, and this agrees with my examples. I had 2x 6BQ6GA/6CU6 GE manufacture that are definitely fat boys. All of my others were 6BQ6GTB/6CU6, and they were the little bottles. I had no GT or GTA that I could find.
Physically, my fat boys are virtually identical to 6AV5 tubes, except for the plate cap.
I also found at least one 6AV5GT in the little 6BQ6GTB size bottle. It was marked KenRad and had dark black rounded plates. I had never seen one of these before.
Win W5JAG
600 Ohm Ots
I think I may try winding one myself since the # of turns should be more reasonable than the usual Hi Z OTs. Probably just wind 8 and 8 interleaved layers of primary/secondary and leave the layer wire ends un-committed. I'm thinking hybrid SS / tube outputs like George tested. Maybe a screen winding for feedback too. Or find an industrial xfmr supply of 480V to 48V xfmrs.
"What are you doing gentlemen?"
I'm saving my old burned out tubes to put Mosfets in the bottles. Will need a little cooling fluid pipe to come up thru the pins though.
Don
I think I may try winding one myself since the # of turns should be more reasonable than the usual Hi Z OTs. Probably just wind 8 and 8 interleaved layers of primary/secondary and leave the layer wire ends un-committed. I'm thinking hybrid SS / tube outputs like George tested. Maybe a screen winding for feedback too. Or find an industrial xfmr supply of 480V to 48V xfmrs.
"What are you doing gentlemen?"
I'm saving my old burned out tubes to put Mosfets in the bottles. Will need a little cooling fluid pipe to come up thru the pins though.
Don
smoking-amp said:600 Ohm Ots
I think I may try winding one myself since the # of turns should be more reasonable than the usual Hi Z OTs. Probably just wind 8 and 8 interleaved layers of primary/secondary and leave the layer wire ends un-committed. I'm thinking hybrid SS / tube outputs like George tested. Maybe a screen winding for feedback too. Or find an industrial xfmr supply of 480V to 48V xfmrs.
"What are you doing gentlemen?"
I'm saving my old burned out tubes to put Mosfets in the bottles. Will need a little cooling fluid pipe to come up thru the pins though.
Wait! I have not bought yet my stock of industrial control transformers!!!
tubelab.com said:
No need to see that many. Long ago I was taught that GT meant glass-tiny. This was the designation for the small envelope with an octal base. The GA designation was for the larger size. and G was the curved version. When you went to buy tube boxes you ordered size by these letters. 7 and 9 pin tubes were known as miniatures.
Victor
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