900 v on a 813 screen sounds high UNLESS the current is very low... better look up the screen dissipation before applying power. 813's were used in RCA AM broadcast transmitters in the 250-500 watt range; I don't recall the screen voltage over 400 with 1250 v on the plates.. (two 813's p-p AB1 modulator, two 813's in parallel for RF...)
Depends which ONES; I think USA/ Russian made 813's would last a long time, the Chinese much shorter.
I found the Chinese 572b's have very short lives, but recently have heard Shuguang has improved them.
Peter Millets 813 Amp
813 SE triode amps
I found the Chinese 572b's have very short lives, but recently have heard Shuguang has improved them.
Peter Millets 813 Amp
813 SE triode amps
I was going to build an amplifier with GM70, but its duration of just 1000-1500 hours blocked me. A tube that could be even better seems to me just the 813. I've done a lot of research on the forums, but nobody talks about their durability. The complaints about the low duration of the gm70 are very frequent. This gives me hope that the 813 has a duration similar to 211 and 845 or at least much better than the GM70.
I have collected almost all my parts for a SE 813 amp. The next hurdle besides settling on a circuit i want to copy, is the output tranny. I hope you, the OP, don't mind me asking what you and others who have built a SE 813 amp are using for the OPT. Can you also specify the primary impedance, the current rating or wattage, and the secondary impedance. regards, 808
Output transformer for what? There was an idea discussed here and several issues were brought up that needed to be resolved, and they weren't resolved. The only schematic I would build that's mentioned in this thread is Pete's triode wired 813 amp, and the output transformers are labeled with the manufacturer and part number on that PDF.
I've been working on am 810 amplifier, and decided to try out some other transmitter tubes. One of them is the 813 driven as a pentode.
I'm attaching the schematic showing measured voltages. It's still work in progress and is probably not optimal since it has grown over time. Thanks to audiowize for his advice nudging me towards the cathode follower for the grid current needs of the 810. The operating point I picked for the 813 puts it close to zero. So I have a 100 Ohm cathode bias on the 813 to bring the grid bias to about -4V. That gets me 120mA of plate current at 800V on the plate and 300V on the screen. The OPT is the Hammond 1628SEA which has a 120mA current limit.
As you can see from the attached THD vs pwr sweep, with 12db of GNFB I'm getting 0.75% THD at 20W and about 1.8% at 30W (max for the OPT).
I've used this setup to test 809, 810. 811A, 812A, 813 and 814 tubes. I'll post the results to another thread once I've finished testing.
Richard
I'm attaching the schematic showing measured voltages. It's still work in progress and is probably not optimal since it has grown over time. Thanks to audiowize for his advice nudging me towards the cathode follower for the grid current needs of the 810. The operating point I picked for the 813 puts it close to zero. So I have a 100 Ohm cathode bias on the 813 to bring the grid bias to about -4V. That gets me 120mA of plate current at 800V on the plate and 300V on the screen. The OPT is the Hammond 1628SEA which has a 120mA current limit.
As you can see from the attached THD vs pwr sweep, with 12db of GNFB I'm getting 0.75% THD at 20W and about 1.8% at 30W (max for the OPT).
I've used this setup to test 809, 810. 811A, 812A, 813 and 814 tubes. I'll post the results to another thread once I've finished testing.
Richard
