No subject

Sun May 13 10:46:53 EDT 2007

Posted by Bill Kleronomos, KD0HG on November 12, 2000 at

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 and


Berthoud, Colo.

Subject: [AMRadio] 813Triode info
Date: Mon, 17 Apr 2000 10:17:58 -0400
From: "Mike Dorworth" <k4xm at>
To: <AMRadio at>

AM Amateur Radio Reflector -

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" <howard.adaire at>
To: "Bob Bruhns" <bbruhns at>
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 <bbruhns at>
> To: <amradio at>
> 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
> > transformer taps for relatively high impedance to the
> > plates.  If you raise the plate to plate impedance, it
> > cause increased screen dissipation in tetrodes and
> > so be careful.  If the plate-to-plate impedance would
> > greatly from typical values, you should reduce the
> > plate voltage and use ordinary impedances instead.
> >
> > This sort of thing is the main reason for any concern
> > 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
> > peak currents, so in most cases the game is to set the
> > impedance such that you are near the optimum power point
> > whatever plate voltages are used in the audio amplifier.
> >
> > If the plate to plate impedance is too high, the tubes
> > not deliver their maximum available current when the
> > pulls down to the minimum voltage, so you get less power
> > output.  In multigrid amplifier tubes, the screen
> > 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
> > out of cathode emission and can not deliver enough
> > 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
> > protective cloud of excess electrons is not present at
> > 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
> > well to that kind of treatment.  All in all, not the way
> > go.
> >
> >   Bacon, WA3WDR

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