Last week's discussion of GG filament chokes got me thinking about modifying my Alpha 77Dx which I believe, ties one side of the filament to the cathode. I would like to cut this tie and user a R.F.
Whoops - my mistake. The 77Dx's 8877 does not tie the cathode and filament together. One side of the filament is grounded. Would it still be advisable to add the common-mode filament choke anyway? -P
Date: Fri, 4 Mar 2005 09:43:00 -0500 (Eastern Standard Time)
Without looking at the best (amp) itself, but knowing that the 8877 has an indirectly heated cathode, no filament choke is needed, only some bypass caps. The heater (filament) only "indirectly" heats
Date: Fri, 4 Mar 2005 10:06:38 -0500 (Eastern Standard Time)
Yup, your right, my faux pas. Should be any time a filament choke is used is on a directly heated cathode. Will --Original Message-- From: Japerlick@aol.com Date: 03/04/05 09:59:56 To: craxd1@ezwv.co
Then why do all the GS35B designs have filament chokes? _______________________________________________ Amps mailing list Amps@contesting.com http://lists.contesting.com/mailman/listinfo/amps
Because the GS-35B has the cathode internally connected to one side of the filament. 73, Tony W4ZT _______________________________________________ Amps mailing list Amps@contesting.com http://lists.c
On first consideration, one might think that the capacitance between the grounded heater and the cathode might shunt some of the drive to ground on the higher bands, making it harder to drive. If thi
Date: Fri, 4 Mar 2005 12:36:13 -0500 (Eastern Standard Time)
Thanks Tony. That's the only exception to the rule. There are some with one side of the heater connected to the cathode. Only a few of these are made that I know of Most either use the heater or a he
between a tube in In the case of the 77Dx (but not the Sx -- see below), it appears quite easy to fully isolate the heater. According to the schematic, the heater transformer secondary is grounded a
While you are 'in the area" check for heater voltage at the tube pins with a good RMS voltmeter. I have never found a 77DX/SX with the proper heater voltage. I assume the transformers were wound for
a Mine too - like 245V. I think a better solution in the initial 77Dx design (and all amp designs for that matter) would have been to use an independent filament transformer to allow for the control
Tying one side of the heater to the cathode - and feeding the (not-grounded) heater through a bifilar RFC is done to prevent an arc from the cathode to the heater in case of a +HV to chassis-ground f
Not if you have a free supply of 8877s. - I would add a bifilar RFC, unground the filament/heater winding, and wire the cathodes to one side of the heater. Richard L. Measures, AG6K, 805.386.3734. ww
Because there is no free supply of GS35Bs. Richard L. Measures, AG6K, 805.386.3734. www.somis.org _______________________________________________ Amps mailing list Amps@contesting.com http://lists.co
A wise decision. I have tested more than one 8877 that had a severed heater wire that was caused by a +HV arc to chassis-gnd. Richard L. Measures, AG6K, 805.386.3734. www.somis.org __________________
Hi Rich For the 8877 at HF you can save the filament choke, a simple gas discharge spark gap at the cathode will fire long before an internal arc to cathode will jump to the filament. The discharge t
I don't know why most manufacturers wont use them but I did see one that did, I just forget who. Who is using those now? A good while back we discussed something similar when I mentioned using bypass
What is the peak-I rating of the gas-discharge device, the V-drop across it at the peak-I rating, and what is its cost? The problem is not a HV arc to cathode, the problem is a +HV arc to chassis gro
Hi Paul, please pass along the information about where to purchase these gas discharge devices and to get more info about them. Perhaps this is what we need for our mid size tetrodes used at 432 and
Gerald, We were discussing those spark gap caps and just spark gaps for use in screen circuits. It's probably in the archive with links to some. Will ** REPLY SEPARATOR ** ___________________________