The 813 Rig Troubleshooting Mystery

[K1JJ]

As my final post for this thread:

Finally - Success!   At 12 Midnight, Don, K4KYV was calling CQ on 3875.  I fired up Hollywood for the first time on the air and gave him a call.

I've spent a few days running tone tests and making some mods to get Hollywood sounding the best I can. I believe a rig can sound excellent before ever seeing real time QSOs.

Don was QSO #1.  He said it sounds exactly like the 4-1000A plate modulated rig. I didn't touch the audio chain, EQ or anything related to audio except the level.  It was a summer night and the shack remained cool. Great tubes, those 813s.

I'm real pleased with the sharp +- 6 KHz  bandwidth audio skirts I see on the receive SDR spectrum, the REA modulation peaks as well as general sound in the mod monitor.  It sweeps cleanly from 19 Hz to about 10KHz. I haven't added in NFB yet due to some circuit mods that need to be done, so it shud get even better.

I put the cover on and consider it a done project for now.  As I was working Don, I was laying out the chassis and front panel for my new 125 watt summertime rig; a 4D32 plate modulated by a pair of 6LF6 big sweep tubes - or maybe plate modulated by a 75 watt SS 8 ohm amplifier using a 1642SE  Hammond  53 Henry 28 pound super hi-fi output transformer. The little rig for summertime.

But for now, Hollywood ran a couple of hours last night without a single problem at 1/2 gallon out. (500 watts)   I have a HV PS that will do 1500-3KV.     2200 V is a great voltage for the lashup.

So there's now two plate modulated rigs in the harem with a third to be added soon.  I shud be on the air with it quite often over the next few weeks, so give me a call.


T

[kc2we]

Years ago, back in 1960 to be exact, I was trying to build a 7094 amplifier out of the 1959 ARRL HB. Newly minted General Class (WA2FNF) I though all I had to do was follow the article. Well, truth be told I never got the 7094 to work in class C or any class for that matter. Gave up and used an 813 with great success. 50 years later, this thing bugged me. So I looked at the 59 HB again. They had the WRONG PINS for all the tube elements. Yikes! Worse yet, there was never an ARRL correction until I pointed out the error in 2015 to the QST editor. What they did was delete the pin numbers in the schematic. There's no way to edit the page from a 1959 document. So, if you use a 7094, a newer version of the 813 (sort of), use the RCA tube manual or Frank's data sheets on-line for the correct pin outs. Who knew.....