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    Building, troubleshooting and testing of these amplifiers should only be
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TV Horz. Output Tubes used as Output Audio

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Damn, another of my secret output tubes discovered.

Unfortunately I spilled my guts about this one in another thread already. I decided to order some tubes from AES since they have them on sale, and another member leaked the goods on one of my "undiscovered " favorites. The 6LR8's were already gone. I did add a pair of 6HJ5's to my order. I will "test" them when they arrive.
 
PB2 said:
I have many, 10 to 20, 6DQ5s that were given to me.

Any experience with these?

Not with those in particular, but with 6BQ6GTBs, and they work very well as PP Class AB1 audio finals. The characteristics of the 6DQ5 are certainly along the same lines: low screen voltage ratings that I would suggest not busting, so that UL or pseudotriode operation is out (though screen drive becomes a distinct possibilty here). Most linear part of the characteristic is unreachable for SE Class A operation, and it was designed to pull bigamps through the horizontal deflection coils.

From eyeballing the plate characteristic, 90W into 600R / Phase looks doable. Of course, getting a 2K4 (P-2-P) 90W OPT might be a bit problematic, and may have to be a custom job. OTOH, Lo-Z OPTs are a good deal easier to design and build and get them to work right.

If you got a bunch of 6DQ65s, I'd say definitely go for it. The 6BQ6GTB turned out to be an excellent audio final indeed.
 
I have a bunch of 6DQ5s I've been meaning to try in my "Miz Piggy" SE screen driven sweep tube amp. I'm using 6CD6GAs at present. The GE tubes I'm using are holding up nicely with nearly 30W of plate dissipation (they're rated for 20), so I haven't felt a lot of motivation for swapping out tubes and fiddling with the bias. The screens on the 6DQ5s appear to be a bit more sensitive, so I expect I'd have to turn down the bias. This amp was an ugly duckling scrap-heap special ( the chassis was free, the output XFMRs are Hammond 125ESEs bought on a whim) that displayed unexpected swan-like tendencies - so much so, that it has been parked in my living room since the last Burning Amp. It'll take a real contender to displace it.
 
The previous posts in this thread were from April. I vaguely remember the 6DQ5 from my TV repair days in the late 60's, but I had forgotten the details. I looked it up. There was one detail that sparked my interest. It carries a 1 or 1.1 AMP peak cathode current rating. Coupled with a low screen grid voltage rating (175 to 200 volts depending on the data sheet) should make this guy a wicked screen drive tube. I stored this information in my (somewhat foggy) memory and decided to look for some at the Dayton hamfest.

While I was in Dayton I spent some time at the ESRC tables just looking through the tubes. I do this whenever I can. Wihile I was there a guy walked up to the table and asked for some 6DQ5's. He was specifically interested in RCA's. This got my interest so I asked what he was building. He replied OTL's. OK cool. Not so cool, he grabbed all the 6DQ5's. I did manage to find a few used ones for $1 each, but I haven't had the time to "light em up" yet.

So we were talking about the 6DQ6B

The 6DQ6 and the 6BQ6 have one unique aspect. Except for the plate cap the pinout is the same as the common audio tubes like the 6L6GC, and KT88. By wiring a plate cap to pin 3 of the socket a 6BQ6 or a 6DQ6 can pe plugged into the same socket as a 6L6GC. NOTE! These tubes do NOT bias anywhere near the usual audio tubes and the screen grid voltage rating is much lower. At least one builder has succesfully used these in a Simple SE. I have also had both tubes working in a Simple SE, but I also exploded a cathode bypas cap due to the need for more than 50 volts of bias. I came to the conclusion that both of these tubes would be better suited to P-P uses since they don't get really linear until the plate is glowing in SE mode.
 
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