813 / 811A AM Rig

[W9ZSL]

I'll be turning 70 on Sunday and I'm at that point where I have to build my "Masterpiece" rig.  I've tossed out a lot of possibilities here in the past, have spent too much and so far have constructed nothing...yet.  On the plus side, the exciter problem is solved.  I'm building a Heath AT-1 from scratch using a combo of original and mostly new parts.

I have a Thordarson T-19P59 transformer that will give me either 3200 or 2560 VCT off a dual secondary. I'd use a choke input filter and power both the RF (813) and AF (pair 811As) into an ART-13 mod iron.  I CAN dial that back with a Variac.

Question: my DC under load probably would be around 1350 to 1400 VDC if I used the higher voltage tap.  The lower one would get me below the ideal of 1250.  If I went with the higher voltage, would the mod iron be happy?  It's NOS, never used.  From what I understand, the nominal audio they can handle is around 110 watts though that rating is really conservative.

My other choice for an amp was more in the 350 watt range but I'd have to build a second supply.  At this point in time, a nice, solid 200 to 220 watt input rig is a logical choice and selling surplus parts works for me because like going to a buffet, sometimes the eyes are bigger than the belly!

Speaking of which, New Year's Resolution #1:  Get cataract surgery so I can see to solder!

[w4bfs]

I have a Thordarson T-19P59 transformer that will give me either 3200 or 2560 VCT off a dual secondary. I'd use a choke input filter and power both the RF (813) and AF (pair 811As) into an ART-13 mod iron.  I CAN dial that back with a Variac.

Question: my DC under load probably would be around 1350 to 1400 VDC if I used the higher voltage tap.  The lower one would get me below the ideal of 1250.  If I went with the higher voltage, would the mod iron be happy?  It's NOS, never used.  From what I understand, the nominal audio they can handle is around 110 watts though that rating is really conservative.

I have heard hams use the art 13 mod xfmr to modulate a pair of 813 @ 2kv or about 600W in ... to do this you have to float the transformer case above ground ... I put one on the hipot test and noted that leakage really started to increase above 2800 Vdc .... you will also need to restrict low freq energy (about 300 Hz and lower) to avoid core saturation ... the om I referred earlier did these things and actually sounded quite good but I don't know for how long .... its tempting but with these becoming harder and harder to find I would limit my application to 1200 v or so

[W9ZSL]

I hear you!  The ART-13 iron is cherry except for some residue from masking tape and a small paint chip.  I got the thing for $19.  Bought new hardware.  I just want to keep this simple. The good thing about the plate iron is I can actually rectify both secondary taps separately.  The problem with that is the mod iron was designed to handle the same voltage for RF and AF. I learned the impedance doesn't matter as long as the voltage is the same.  Realistically, I think I'll end up with 1350 VDC and I doubt the iron will care.  The tubes certainly won't.