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RCA 6146B sub for 807 or 6L6?

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Wigwam Jones

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Joined 2011
#1
I managed to acquire a pair of RCA 6146B tubes recently, and I'm interested in building a single-ended stereo amp with these as output tubes.

I have read through every thread I could find on the 6146B on this and various forums, including warnings and caveats about non-linearity, large disparity between plate and grid voltage, and so on.

However, it appears that at least some folks feel that one can build such an SE amp, good for perhaps 10 watts output, by using a schematic for an 807 SE amp. Trouble is, I've yet to find one that looks like I could build it. That is, simple and not requiring expensive components. I have also read comments that a schematic for a 6L6 would probably work.

So I'm soliciting opinions at this time. I have not committed on any particular course of action, and I'd have to pick up a couple parts anyway (like top caps for the anode) before I could build anything. But if you have a link to a nice, basic, no-frills, SE schematic for an 807 or 6L6 that would work with this RCA 6146B tube, I would sincerely appreciate seeing it. I have googled left right and center, but nothing has really seemed to jump out at me; perhaps I am missing something basic in my searching.

Also, if I am making some unwise assumptions or missing some dreadful bit information, please let me know that as well! 😀 I am very much the basic newbie at this.

Thanks ahead of time!
 
#3
I have an RCA PA amp that uses 6146A's which I rebuilt,,, don't think I'd build anything using them,,, but if you already have em!!!!!
I'm building an amp with 811A's,,, so, I guess anything is possible!.... I couldn't help you with a schem, tho,,, The RCA uses 0C3 regulators for teh screens, and I believe 580V Vp, IIRC,,, but thats 70W PP...
Be interested in what you come up with, I'm sure you can get help here...
Good luck...
 
#6
Sell them to a ham radio operator who can use them.

Get some tubes that are actually useful for SE operation.
With a minimal amount of effort you can come up with not very expensive tubes.
The output iron is far more important to the final result and also likely more expensive than the lower cost tubes that are suitable for SE operation.

The chinese tubes and russian tubes are really not terribly expensive, for example EH300b work nicely and are not particularly pricey.

Given all the work and effort required to build an amp from scratch, one might as aim higher than just "what's in the junk box". Unless you have a junk box that is more like a surplus store... 😀
 
#7
bear said:
Sell them to a ham radio operator who can use them.

Get some tubes that are actually useful for SE operation.
With a minimal amount of effort you can come up with not very expensive tubes.
The output iron is far more important to the final result and also likely more expensive than the lower cost tubes that are suitable for SE operation.

The chinese tubes and russian tubes are really not terribly expensive, for example EH300b work nicely and are not particularly pricey.

Given all the work and effort required to build an amp from scratch, one might as aim higher than just "what's in the junk box". Unless you have a junk box that is more like a surplus store... 😀
Click to expand...

I have quite a few fun tubes of various sorts, and I am amusing myself building small amplifiers with them on weekends. Sometimes I like the results and sometimes I do not, but I am learning a lot. I generally disassemble when I am done and move to the next set of tubes, although some I am planning to put into a chassis at some point.

I know some folks who climb mountains. I have no idea why they would do such a thing, when we have perfectly good cars and helicopters to take them to the top if that is their goal. Perhaps they climb because that's what they want to do, rather than simply getting to a destination? Consider me a climber, then, rather than one with a goal in mind. It is less "I want to build a great amplifier" and more "I want to try to build an amplifier with these tubes for the joy of the challenge."

Humor me, if you would be so kind. I am quite aware that there are better ways to do it, but that does not mean it should not be done. Sometimes it is fun to do something off the beaten track simply for the sake of doing it.

...And FYI, the EH300b tubes you mention are very nice, and 'pricey' is a relative term. Certainly they *are* pricey by my means. I spent less than 2 US dollars on these 6146B tubes. I sincerely doubt I could obtain a pair of EH300b for 2 dollars.
 
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#8
I was under the impression that the 6146 tubes were not really suitable for SE operation. I have been known to "test" tubes at their limits and run them in unintended applications, but I have never tried the 6146 in SE.....But there is someone who has. A ham radio guy has stuffed more unusual tubes in his SSE board than I have. See this thread.

http://www.diyaudio.com/forums/tubelab/173622-6146-simple-se.html


Note:

Way back in 1969 I had an old Emerson color TV. The 6CB5 horizontal sweep tube was dead, and I didn't have one, so I wired in a 6146A and it worked fine. The 6146 works more like a sweep tube that a 6L6 type. Do not feed 300 volts or more into the screen grid, or your amps will blow up just like the old Ampeg SVT's did.
 
#9
tubelab.com said:
I was under the impression that the 6146 tubes were not really suitable for SE operation. I have been known to "test" tubes at their limits and run them in unintended applications, but I have never tried the 6146 in SE.....But there is someone who has. A ham radio guy has stuffed more unusual tubes in his SSE board than I have. See this thread.

http://www.diyaudio.com/forums/tubelab/173622-6146-simple-se.html


Note:

Way back in 1969 I had an old Emerson color TV. The 6CB5 horizontal sweep tube was dead, and I didn't have one, so I wired in a 6146A and it worked fine. The 6146 works more like a sweep tube that a 6L6 type. Do not feed 300 volts or more into the screen grid, or your amps will blow up just like the old Ampeg SVT's did.
Click to expand...

Thank you, I'll read that thread very carefully. Somehow I missed it when I was googling for circuits.
 
#10
As Tubelab correctly states, if you treat the 6146X family as a 6L6 or 807 type, you will run into problems pretty fast. I don't know where that notion got started, but it's just plain incorrect in my view. For audio use, it needs to be thought of as a sweep tube and ran as a pentode. If you don't want to use the SSE board as a base, I think you would be better served by looking for schematics for tubes like 6BQ6 or 6DQ6 and adapting from there.

My experience, over many thousands of hours of using 6146, is that it is very satisfactory as a single ended pentode. I still have my 6146 amp running in triode service out in my radio room. There is now the beginning of a second thread down in the Tubelab forum regarding triode service of the tube. I've only begun to explore that because of the severe constraints on my time these days, but my preliminary view is that triode service is pretty much a dead end. Pentode is likely the best way to go with that tube.

Good luck and let us know how it goes for you.

Win W5JAG
 
#12
I haven't tried it in ultra linear, so you will be plowing new ground there. If you do that, let us know how it works out.

I do think 280 volts is too high on the screen, you will want 63 volt cathode caps at a minimum. I went around 205-210 volts on the screen on mine. These tubes also work very well in the VHF range, it was a big application for them, you need to take care they don't oscillate on you.

edit: also, that grid resistance is too high. I don't know what the correct value is. I settled on 100K.

Win W5JAG
 
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#13
w5jag said:
I haven't tried it in ultra linear, so you will be plowing new ground there. If you do that, let us know how it works out.

I do think 280 volts is too high on the screen, you will want 63 volt cathode caps at a minimum. I went around 205-210 volts on the screen on mine. These tubes also work very well in the VHF range, it was a big application for them, you need to take care they don't oscillate on you.

edit: also, that grid resistance is too high. I don't know what the correct value is. I settled on 100K.

Win W5JAG
Click to expand...

Thanks very much! I don't know if I will go UL either; none of my current small stash of cheap OPTs have UL taps. Of course, none of my OPTs can handle the power the 6146B tube can deliver, either, so I guess I'll have to buy some, even for experimentation purposes.

I tend to overspec parts, as I am paranoid and a little extra spec never hurt anything. I watch the parts houses for overstock sales and I'm well-stocked with 2 watt resistors in place of 1/2 watt, 650 VDC caps in place of 63 VDC, etc. Better safe than sorry; I've already inhaled too much burned resistor smoke.

I have a couple PTs that have more than one HV winding, so I can probably develop B+ for the screen within parameters without having to resort to extreme measures to drop the B+ for the plate to suit. I presume that will do the trick, although it means two sets of rectifiers and power-smoothing CRC sections.
 
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