Hello Howard, I never ran 813s in triode connection, but here's what I have on the subject, from AM posts by Bill Kleronomos, KD0HG, and Mike Dorworthm K4XM.
Also I believe the series screen grid resistor idea (about 4.7K unbypassed to each screen grid) should work with 813s in tetrode connection, if you want to play with that. Just be careful if you try it; if there is serious secondary emission, the screens won't behave as they need to for that mode of operation. But I think it will work. This hookup wants the same plate Z as comparable tetrode operation, but maybe 50V more is needed from the screen supply, which should be regulated, and slightly more negaive control grid bias to compensate for the higher quiescent screen voltage. Try different screen resistor values for minimum distortion. Bacon, WA3WDR --------------------- >From The AM Window website (www.amfone.org) Re: 813's as triodes Posted by Bill Kleronomos, KD0HG on November 12, 2000 at 23:09:44: The specs for triode connected 813s are : Max Ep= 2500, P-P load =~15,000, power out = 550W. Depending on the plate voltage, you'll need a few volts of bias which can be provided in the conventional manner. The u of a triode-connected 813 is 8.5. The exact P-P load Z and match isn't anywhere as important as the turns ratio between your mod transformer windings. To triode connect, tie G1 and G2 together and treat as one control grid. You can ground G3 and the internal shield. Look for a mod transformer (and any associated reactor)out of a 250-1000 watt broadcast transmitter, for starters. The iron out of a BC-610 or a T-368 would also be useable, but not quite as hi-fi at full power. A good resource for broadcast transmitter parts and contacting people that might have good junque is www.broadcast.net and http://radio-classifieds.com/classpro/viewads.html luck Bill Berthoud, Colo. Subject: [AMRadio] 813Triode info Date: Mon, 17 Apr 2000 10:17:58 -0400 From: "Mike Dorworth" <[EMAIL PROTECTED]> To: <[EMAIL PROTECTED]> AM Amateur Radio Reflector - http://www.bigcountry.com/w5ami Information on 813(T) found in ER 5, ER 15, ER 57. Calculated information (EXACT Values) to modulate 500 watts DC input @ 2250 VDC. 312 1/2 watts needed. 357 peak Ma, 114 mA Average. Plate to Plate load 19608 ohms 60 volts to grid (grid to grid 120 volts) Peak grid current 100 mA Driving power 3 watts. Tube voltage drop 500v at 0.357 amp peak. ----- Original Message ----- From: "Howard Aspinall" <[EMAIL PROTECTED]> To: "Bob Bruhns" <[EMAIL PROTECTED]> Sent: Friday, July 05, 2002 10:47 AM Subject: Fw: [AMRadio] 807's triode connection question... > Hi Bacon, > > This topic is all very interesting. I'm currently making > something using two pp 813 tubes in class B connected > the similar way as described for 807s. The books I've seen > on the subject give little or no info on this arrangement, > especially anode to anode resistance which presumably > differs from values for conventional class B for tetrodes. > > For instance for the 807 tube the 4th edition of the RSGB > Radio Communication Handbook gives the load resistance > in class AB1 with 750v plate voltage as 7k ohms and for > triode connected class B with same plate voltage as 6650 > ohms > > I'm planning to drive the 813s from a valve hi fi > amp giving up to 50 watts out at 15 ohms, into a > hi fi o/p tranny connected in reverse as driver > tranny for the class B amp. > > Is there any available history or info on use of > 813s in this application, and is there any easy > way of calculating or anticipating the anode to anode > resistance of the tubes used this way. > > This may be interest to otherss on the AM list, > so feel free to quote my message, if appropriate. > > I'm still experimenting with negative cycle loading > etc with super results on 160m > > 73..Howard/G3RXH > > > ----- Original Message ----- > From: Bob Bruhns <[EMAIL PROTECTED]> > To: <[email protected]> > Sent: Thursday, July 04, 2002 4:55 PM > Subject: Re: [AMRadio] 807's triode connection question... > > > > Hi Vince, > > > > Use lower modulator plate voltages, and/or set up the mod > > transformer taps for relatively high impedance to the tube > > plates. If you raise the plate to plate impedance, it will > > cause increased screen dissipation in tetrodes and pentodes, > > so be careful. If the plate-to-plate impedance would differ > > greatly from typical values, you should reduce the modulator > > plate voltage and use ordinary impedances instead. > > > > This sort of thing is the main reason for any concern about > > impedance in a classic power amplifier. The impedance > > presented will affect the current that the amplifying > > devices will draw. There are limits to maximum voltages and > > peak currents, so in most cases the game is to set the > > impedance such that you are near the optimum power point for > > whatever plate voltages are used in the audio amplifier. > > > > If the plate to plate impedance is too high, the tubes can > > not deliver their maximum available current when the plate > > pulls down to the minimum voltage, so you get less power > > output. In multigrid amplifier tubes, the screen current > > will be higher because the plate voltage is lower during > > conduction. However, it is much better for the tubes to > > present a somewhat higher-than-optimum load impedance. > > > > If the plate to plate impedance is too low, the tubes run > > out of cathode emission and can not deliver enough current. > > They then flatten out (and distort) at high current at > > relatively high plate voltage (they can't pull it down > > enough). Plate dissipation is high because of the high > > voltage-currrent product, and also the cathodes are > > exhausted in the overloaded peak condition, and the usual > > protective cloud of excess electrons is not present at those > > instants, so the cathodes are exposed to ion bombardment > > damage because there is still considerable plate voltage > > present at those times. Oxide cathodes really don't respond > > well to that kind of treatment. All in all, not the way to > > go. > > > > Bacon, WA3WDR > > >
