You can right click on the schematic and then select "save as", it will D/L from my web space into your pictures folder as a JPG...

It's over 400Kb should be plenty viewable...

Tom

Ack!

Just checked Goldmine - these (rather neat) transformers are now sold out.

Item: G12951


Not so much of a matter, as I'm sure a 24V could be rigged to work pretty well...

Mike Y

That's what I get for late-night reading...I should have known that if you were talking about the tube modulating better, you would probably be talking about the only tube that does modulation in the circuit: the 12CS6. I might experiment a bit with the cathode biasing in the 12AV6 at some point soon and see what difference that makes. In terms of operation, what does the cathode resistor setup do that the "normal" grounded cathode setup doesn't? I vaguely remember something about how this all works out, but I don't remember the theory at the moment...

-Dan

I do have 12CS6 sylvanias pre-tested by 35Z5 in stock.

I do have 12CS6 sylvanias pre-tested by 35Z5 in stock.

I do have 12CS6 sylvanias pre-tested by 35Z5 in stock.

I do have 12CS6 sylvanias pre-tested by 35Z5 in stock.

I think 12AT6 is equivalent of 12AV6 and was in many AA5's also. Newbies and lurkers might not know this.

Just so that everyone knows the 12AV6/12CS6 is the only Leal/Bryant xmitter kit that I'm stocking at the moment. (they are all from the original Leal 6888). It's the best ever though and they came up with this one together. A leal xformer and the rest by Bryant. I've got a 12v on the back burner from a 35Z5 schematic but with a battery power supply. Members are prototyping that one as we speak. Latest order for the 12AV6/12CS6 was from Bluestar.

What's the current draw on the B plus?

http://www.chaneyelectronicsstore.com/s ... mer/Detail

Chaneyelectronicsstore.com has some G12951 transformers.

Less than 20ma...

BTW Norm & I determined the G12951 xformer's 36v winding is closer to 500ma(if that) than the rated 750ma, the 24v winding does appear to be correctly rated... This is of no issue for this Tx but if you plan on using one for another project, it's something to consider...

Tom

The G12951 transformer might be capable of delivering a maximum of 500mA on the 36V winding, but I was wondering what the actual current draw was on the B+ side of the transmitter.

In other words, if a milliampmeter is placed in series between R9 & the B+ supply side, what is the current reading?

Less than 20ma...

Tom

Thanks Tom. That's about what I thought it was going to be, but I wanted to make certain. I was searching a subsitute for the G12951 transformer, but now it appears that the G12951 is still available.

It occurs to me that the gain before distortion might be improved a bit if C1 was to be decreased in value to roll off some of the low frequencies. I've noticed that the lows seem to be what overdrives the preamp the most. If C1 was, for example, .001 uF, and the resistor after it was kept at 3.3M, the corner frequency would be about 60 Hz. Is the value of C1 particularly critical to the grid input or is it just there for DC blocking?

-Dan

Most likely there for dc blocking.

Yep, just for DC blocking...

When I checked frequency response with the sweep gen, it was linear using a .02-.05, so that's what I've been using but if you want to reduce the value to cut lows that's fine...

Because many sources do vary in amplitude, I try to keep my xmitt at around 80-85% modulation so if that extra low frequency comes boomin' through, it doesn't distort... A limiter would be a good addition if you'd like to continually modulate at 100%, but there is very little difference in loudness between 80 & 100%...

I did use a compressor/limiter but switched to a $15 Craigslist computer with XP and Windows Media Player to supply all my material... Most don't know it but version 9-up players in XP(not earlier operating systems) have a volume equalizing feature built in, it isn't as good as the limiter but works OK for me...

Tom

I'm getting ready to assemble the 12AV6-12CS6 transmitter kit, and I have a trimmer cap with a range of 18.5pF-73.4pF. Is that within the parameters for VC1?

Well that's less than I generally use but if it doesn't peak due to not enough capacitance, add a 47 to 68pf across it and try tuning again, if that won't do it add a second... I've had a similar setup with a padder cap for tuning in my 12AU7/6GY6 Tx for almost four years...

Tom