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 Post subject: 6146 for audio output tube ?
PostPosted: Sep Tue 05, 2006 5:01 am 
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Location: Rochester, NY USA
I picked up a batch of 6146 tubes at an estate sale - has anyone used these as audio output? The RCA manual shows Class C modulator service as an application, but doesn't reference audio output. It appears that a P/P pair could handle some serious wattage.

David


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PostPosted: Sep Tue 05, 2006 5:12 am 
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Ampeg used them in the SVT amp, but later changed to the 6550. Low screen voltage is a problem - can't run them in ultralinear without a separate screen winding.


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PostPosted: Sep Tue 05, 2006 7:27 am 
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Acrosound made a transformer, as Tom described, with a separate, tertiary winding for 6146 screens. It was the TO-350. I believe they are rare.

David - I've emailed a schematic and data to you.

--Chuck


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 Post subject:
PostPosted: Sep Tue 05, 2006 1:28 pm 
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Thanks Chuck,

Received the email and attachment and will spend some time studying these circuits. I appreciate the information!

David


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 Post subject:
PostPosted: Sep Tue 05, 2006 1:59 pm 
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IIRC it was RCA that built a theatre amplifier with P-P 6146's back in the 50's or early 60's, which was rated at something like 75 or 100 watts output.

Like nearly any other beam power tube or pentode, they would make good audio output tubes provided you get the magic combination of load impedance for fidelity and bias so the tubes don't self-destruct.

The '63 GE manual does give some specs on audio amplifier applications for the 6146 and 6146A. I would want full data sheets before trying to design anything, but I suspect you wouldn't be far off by using a proven 6550 design and reducing G2 voltage accordingly.

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Experience is what you gain when the results aren't what you were expecting.


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PostPosted: Sep Wed 06, 2006 11:37 pm 
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Right you are RCA did make a 70 watt theater amplifier in the fifties, or perhaps earlier. I have three of them. One had been converted to 6550s, and I converted it back to 6146. Thjy're easier to find than 6550s. Those amps used the abominable Black Beauty striped capacitors.

The amplifier is no sensation for fidelity, butr decent sounding, nonetheless. Nice thing about 6146, you can drive them to full power with a 12AU7.


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 Post subject:
PostPosted: Sep Fri 08, 2006 12:30 am 
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I worked on many of those RCA amplifiers; they were quite popular in drive-in theatres. RCA did have a retrofit to change the 6146 tubes to 6550s, which was done because they were having parasitic oscillation problems. The 6146s would turn "cherry red"! The bias had to be changed when the conversion was made. In some systems, those amps were driven pretty hard. RCA used gas regulator tubes on the screen grid supply.

The 6550 worked a lot better, but it's getting to be a pricey tube these days. They are used in some big Ampeg and Peavey guitar amps, and in the amplifier in many Leslie speaker systems.

Tim


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 Post subject:
PostPosted: Sep Tue 12, 2006 5:15 pm 
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Location: Austin Texas USA
David, et al...

A curiosity...

Although I had not been familiar with the 6146 beam power transmitting tube employed commercially as an audio output tube, another beam power transmitting tube, the 807 has had some favor among small-time audio amp builders...Four such tubes, run as triodes in parallel, p-p has been a subject of some discussion for a number of years...Considering that 1625's are nearly the same tube (pin-out and heater voltages different) and are furthermore plentiful and comparatively cheap, I wonder if this tube might not be a suitable alternative for a homebrew audio enthusiast.

Bruce
WC5CW


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 Post subject:
PostPosted: Sep Tue 12, 2006 7:47 pm 
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Keyop wrote:
Although I had not been familiar with the 6146 beam power transmitting tube employed commercially as an audio output tube, another beam power transmitting tube, the 807 has had some favor among small-time audio amp builders...Four such tubes, run as triodes in parallel, p-p has been a subject of some discussion for a number of years...Considering that 1625's are nearly the same tube (pin-out and heater voltages different) and are furthermore plentiful and comparatively cheap, I wonder if this tube might not be a suitable alternative for a homebrew audio enthusiast.

Bruce
WC5CW


For some time I have considered building a pair of Williamson type amplifiers, using 1625s and 12SN7s, which are much cheaper than 6SN7s. The sockets for the 1625s are somewhat harder to find than for 807 or some octal tube, but I have those already, along with the tubes and output transformers. I need to find a cheap pair of power transformers and will probably need to use separate filament/heater transformers. I can wait until I find a buy on something, since I want to be able to brag about how little I spent on the whole project.

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 Post subject:
PostPosted: Sep Fri 15, 2006 10:45 pm 
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I saw 6146's in RCA amps used for PA systems (building wide) in schools. They also are familiar to ham operators as modulators.


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 Post subject:
PostPosted: Oct Sun 08, 2006 7:31 am 
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Can't remember th' name of it; I had one here for a spell - think it was a Thordarson kit amp - used a pair of 807s!


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 Post subject:
PostPosted: Oct Sun 08, 2006 7:32 pm 
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Location: Lakewood, California
Da Duffer wrote:
Can't remember th' name of it; I had one here for a spell - think it was a Thordarson kit amp - used a pair of 807s!


Very possible--Thordarson did offer kits for amplifiers, receivers, transmitters, etc.

Maybe you were thinking of the Stancor kit amp that used 807's? It was a 2-piece amp (separate power supply). Stancor supplied the transformers, chokes, pre-punched chassis and a detailed parts list. First version was a Williamson circuit, with a later "Ultra-Linear" upgrade available.

Years ago, I ran frequency response curves on the 2 Stancor Ultra-Linear amps I have and they performed up to Stancor's specs. Just for kicks, I changed one of them from 807's to EL34/6CA7 output tubes with a noticeable loss of low frequency response. Probably due to a mis-match of tube to transformer, I never did investigate further.

Triad also offered kit amps from 3 watts to 40 watts. I have the model HF-18, with KT66 output tubes (same amp /transformer could use 807's).

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 Post subject:
PostPosted: Oct Thu 19, 2006 12:28 am 
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Essentially it's the evolution of the same tube. The 6L6 was the predecessor to the 807 and 1625, which were later modified to the smaller envelope of the 6146 for higher frequency performance. 6146s are OK as modulators, but better as RF amps.


Scott Todd


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