807 tube connected low u (scr to plt) operated at 600Vdc in a wilcox 99 xmtr

[w4bfs]

I have verified the unit is wired with the 807 screen tied directly to plate as a low u driver.  the Wilcox 99 modulator is a type 95479 and is unusual in several regards .... 600 ohm bal audio in to balanced 6sn7 stages with the second using a 1:1 interstage driving the 807 control grid ref to gnd.....  the 807 is cathode biased with a 750 ohm resistor, unbypassed... B+ listed as 600V .... the 807 pp stage then drives 813's connected high u triode again cathode biased ref to ground

Rca spec's 807 with screen tied to plate as 400V max in AB operation .... I always thot Wilcox supplied stuff like FAA xmtrs and was conservative in design ... I am going to test the last IT for turns ratio and I suspect it may have part of the answer

Has anyone seen this before?

added 11:40 am   tested turns ratio of the 807 / 813 IT .... found a 2:1 ratio .... this seems correct as Rca specs the triode connected pp 807 at 3kohm ..... this yields a sec total impedance at 750 ohm and a lot of V swing

[KE6DF]

The BC-1E had a somewhat similar circuit.

An input transformer, followed by two 6V6's triode connected as you describe, followed by two 845's followed by a pair of 833 modulators.

All transformer coupled.

I have a mod driver deck with the 6v6's connected this way. You can also plug in a 6B4 and use that for the first stage.

I think triode connected 807 are very similar to a pair of 2A3s or 6B4s.

The BC-1E needed the extra 845 stage to get enough drive for the 833s.

[w4bfs]

The BC-1E had a somewhat similar circuit.

An input transformer, followed by two 6V6's triode connected as you describe, followed by two 845's followed by a pair of 833 modulators.

All transformer coupled.

I have a mod driver deck with the 6v6's connected this way. You can also plug in a 6B4 and use that for the first stage.

I think triode connected 807 are very similar to a pair of 2A3s or 6B4s.

The BC-1E needed the extra 845 stage to get enough drive for the 833s.

Cadillac

[W3RSW]

As is the Super Pro in the receiver world.  6f6's triode connected.

"when 6C5's won't do the driver job, then strap your way with 6F6's."

[W2PFY]

have verified the unit is wired with the 807 screen tied directly to plate as a low u driver.  the Wilcox 99 modulator is a type 95479 and is unusual in several regards .

You must have such a beast? I would love to see some pictures of it if you have any You don't hear of people very often running or even having a Wilcox transmitter?

I know they had a model that used two 250TH tubes in it and another that used 450TH tubes. I think they were for air to ground and for ground to ground transmissions.

Thanks Terry

[w4bfs]

You must have such a beast? I would love to see some pictures of it if you have any You don't hear of people very often running or even having a Wilcox transmitter?

I know they had a model that used two 250TH tubes in it and another that used 450TH tubes. I think they were for air to ground and for ground to ground transmissions.

Thanks Terry

Hi Terry .... you can google Wilcox 99 transmitter and get the sales page, all 4200 ibs of it 

We (k4ndy) and myself are going to use the audio modules from the modulator for each of our TMC GPT 750 re-dos ... Sam sez if Wilcox did it, it must be ok ... I wish I had that kind of credibility 

[w4bfs]

thanks to all who  took a look .... looked at the curves and table data from Rca tube manual .... everything in the as-built lines up for 400 V operation ... looking at the curves and placing the load line gives a 200 V peak plate swing .... transforming this down should give a 100 V 813 grid(s) peak swing .... this is more than the 65 V spec'd by Orr so is conservative and gives a reserve as the 807 emission drops

conclusion: I've learned that Vendor (Wilcox in this case) data is not always right ... if you smell a mouse, check yer mousetraps