Have 6146B tubes been used in high fidelity power amps?

hammr7

hammr7

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I came across a stash of NOS 6146B tubes I picked up ages ago. I thought I remembered a few high powered tube amps that used some variation of the 6146. A quick search showed they were very popular in HAM transmitters, but I didn't see anything truly hi-fi. Given that I have 15 of them, what can I build?
 
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The 6146B was used in the early versions of the famous AMPEG SVT bass guitar amp but they later switched to the 6550 due to some reliability issues. The rather low Ug2 max.ratings of 250V is a limiting factor and doesn't allow using the 6146 in U/L circuits, but it is a very sturdy tube and with a stable (regulated) screen supply you can easily get 100 watts audio power from a pair in cl. AB PP. I'm not aware of any commercially produced Hi-Fi amp using this tube but there was a circuit of a 90 watts (Hi-Fi) amp called "The Maestro" described in the Nov.1952 issue of Audio Engineering. You can have a look at it here (starts at p.19):

http://americanradiohistory.com/Archive-Audio/50s/Audio-1952-Nov.pdf

It would be a great project if you have a small stock of N.O.S 6146B tubes available.
 
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I was reading that article. Thanks for the link. Making a regulated supply with sand today is easier than it used to be. Maybe I'm reading into it but I'm thinking a variant of Dave's EFB would be exactly what the doctor ordered for this.
Hank ,
If you're looking for a cool project, clearly this is one. But by the time you get proper iron and bits together, probably won't be cheap (even figuring the no cost outputs).
Also unlike a Marantz, Mac, Acrosound, Fairchild vein(this being a one off), if you wanted to sell in the future it'd be harder to make back your investment .
Good luck with the project!
:lurk:
 
Screen regulator would be easy, EFB or just straight up fixed voltage would get you there. SS or gas regulator tube if you have the space and like the glow.

Another way around it, presuming you were OK with B+ at 500, is to use a voltage doubler supply and tap the screen at the mid-point. Dave's re-work of the Bogen MO-200 works that way. It does make the screen supply half-wave rectified though. The MO-200 re-design involves a choke on the screen supply to smooth this out.

Another way is to do it like my Bogen DS-225 does, which is a pair of HV supplies in series with the screens tapped from the mid point. The 225 has a pair of 5AR4's in series, with the screens tapped off the first one and the plates off the second. There are two HV windings and two rectifier windings to get this done though, so you'd be looking at a custom transformer most likely. Both of those methods let the screen voltage track with plate voltage, which is what EFB gets you.

Bogen used an active pentode regulator on the DB-230 (I think the 130 and 230A used this too) to cap the screen supply for the weirdo sweep tubes they used on that design. I suppose you could make this track voltages like an EFB screen regulator as well, depending on where you tap your voltage reference source. Functionally there wouldn't be any advantage to this over using a power MOSFET, and it would probably be easy enough to make up a list of reasons to not do this even though it would get the job done.

Fisher used an HV winding on the TA-600 with two sets of taps, the lower voltage set went to a rectifier to feed the tuner, the HV set went to a high current rectifier for the power amp stage. Its a single HV winding though, one feeding a 6V4 that lights off the regular heater string and the other running a 5AR4 with it's own heater winding.


Many ways to skin a cat as they say :) Some aren't super practical though since it would involve custom transformers. The practical way is probably an SS regulator device off a conventional HV winding.
 
Thanks for the quick responses! As I organize and downsize I'm trying to figure out what may be project-worthy in the future. Among my boxes of Ham and Broadcast tubes I guess the 6146Bs will be keepers. The project won't be near future, but at least I know there are possible uses.
 
Keep in mind there are four different 6146 tubes I've come across... 6146, 6146A, 6146B, and 6146W... some of them don't interchange...
 
I know the "B"s aren't a drop-in replacement for the originals or the "A"s (although the originals and "A"s can usually replace a "B" at lower pwer output). The "W"s were originals or "A"s until the mid-60's, at which point they were ruggedized versions of the "B"s.
 
The RCA engineer who designed the 6146 amps would have rather used the new 6550. RCA management decreed use of their 6146. He uses 6550's in his own amps...:)
cheers,
Douglas
 
I think the 6146 is a fine tube for hi-fi applications.The 6146 is an extremely rugged tube,both physically and electrically.Like all tubes,if you respect it's specifications,you will get good service. If you run it at the ragged edge of it's limits,you won't.The 6146 has two sets of specs, CCS and ICAS. The reliability issues Ampeg experienced with this tube were caused by players overdriving (often for extended periods!) the amplifier,which did not respect spec chosen for the design.The upgraded specs and easier availability of the 6550 were an obvious and necessary choice. Luckily for them,the operating points were similar enough to permit this change.

I have converted several early-era SVT's to 6550's,but I ( and most of my customers ) honestly preferred the sound and ''feel'' of the original output tubes.
I used a 6146-equipped SVT for a long time,and had no failures on the road whatsoever.And those power tubes seemed to last forever. Mind you,I never used it as a 300 watt fuzz-box. I now use a later (1978:rflmao:) 6550 model,and it really is not the same.

Just for the heck of it,I've been wanting to try the 6146 in my older D-series Audio Research amps,as the G2 supply is regulated and the voltage is easily changed.
Where will I ever find the time......
 
I had a set of Acro TO-355s (same as -350 w/ high-Z taps). I ended up trading them away long ago. That person tried to build the amp in the bottom schematic. IIRC, he could never get it to run correctly as a UL and eventually built a dedicated screen supply. When I searched for the Acrosound schematic just now I found the Sarser Maestro version. Did not know that there was a 6146 variant for that amp. I associate 807/350A/350B for it in the finals but see it has a dedicated screen supply (hmmmm, older / wiser etc.) -

Maestro%206146_a.jpg



Acrosound-6146.gif
 
Guess I should just list the other broadcast / industrisl tube types I have quads or more of to see what kind of audio attempts there have been! :bigok:

Anyone done anything with 6850 or 6884 tubes?

I have a bunch of 6989, 7021, 7023 and 7786, but these all seem to be rectifiers from hell.
 
That TO-350 is an interesting transformer. Not very many transformers would allow completely different screen and plate voltage supplies and still be ultralinear compatible.
 
The 6146 seems to be a great tube for folks like us that like to experiment or roll our own designs,and therefore don't have to worry about easy,off the shelf availability. Not only do they come in a multitude of heater voltages,they were also made in a quick-heating filament type for mobile applications. Were it not for the screen grid voltage requirements,I really think a quad of these plate-cap stubbies would look great in a McIntosh 275.
 
gadget73 said:
That TO-350 is an interesting transformer. Not very many transformers would allow completely different screen and plate voltage supplies and still be ultralinear compatible.
Click to expand...
The TO-350 gives the same 'U-L' effect if you hook the cathodes to the extra winding, and leave the g2 supply fixed to ground. The drive requirements and output Z are *QUITE* different.
cheers,
Douglas
 
Interesting. My Bogen DS-225 has dual windings on the transformer too. In stock form one goes to plate, the other goes to the cathodes. I guess perhaps its getting some UL effect as well.
 
U-L gives a fraction of the plate-cathode change to the g2...in the case of the CFB rigging, and fixed g2, the cathode is moving towards( or away from) the g2...instead of moving the g2 as the original U-L did...:)
 
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