QIX:Converting an EICO 720 to use a 4D32 in your screen grid mod circuit

[w1vtp]

Steve

RE:  http://amfone.net/Amforum/index.php?topic=26603.0

I wonder what I would have to do to convert one of my EICO 720s to use a 4D32 for use of your screen grid modulator?  I think the additional power would give plenty of reserve for driving my AL82 for good positive peaks

Al

[N2DTS]

Will it fit?
The 4D32 has a much larger base...

In a qso today, someone said something about converting a viking 1 to screen modulation.
It had a 4D32 and a poor modulator I guess.

A pair of 4D32's would get you 100 watts carrier...

[steve_qix]

Hi Al,

The physicality of making such a modification is going to be the greatest challenge.

Do you have a Viking I or II?  If so, it would probably be simpler to create a "drive a linear mode" where the RF amplifier is screen modulated.  A good screen modulator is simple using a couple of MOSFETs, and will work superbly well.

[fg5fc]

Good afternoon Steve

Could you post such circuit using the 2 MOFSETs wicth you spoke about?

regards

[w1vtp]

Hi Al,

The physicality of making such a modification is going to be the greatest challenge.

Do you have a Viking I or II?  If so, it would probably be simpler to create a "drive a linear mode" where the RF amplifier is screen modulated.  A good screen modulator is simple using a couple of MOSFETs, and will work superbly well.

Yeah, the 4D32 would be taller and fatter.  The approach would be to  do the "sunken garden" approach in the 720 where the tube base would be lowered so that the top wouldn't stick up too far, also, a bigger hole would have to be cut to accommodate the diameter of the new tube.

Good thought on the Viking 1 or 2.  If I ever blow the modulation transformer in either my 1 or 2, instead of replacing the transformer one could install your screen grid modulator. Space formed by removing the modulation could be used for the SG modulator - in a vertical configuration.

[steve_qix]

You could put the screen modulator circuit into the transmitter in any event.  That would give you a "low power high fidelity mode" that you could use with a linear amplifier (or just run low power).

Essentially, the rig is operated in the CW mode, and then another switch enables the screen modulator.  The screen modulator does not need to take up a lot of space.  The whole thing can be accomplished with a couple of MOSFETs and either an op-amp or some small discrete components.  It would all fit inside of the transmitter.

[N2DTS]

Or you can use the tube circuit Steve came up with, it sounded fantastic to me, as do many other of the dx60 type screen modulators.
I like the idea of just two 9 pin tubes in the audio section, D104 in and good audio out.

The 4D32 is not a tall tube, but its wider.
There are sockets that are recessed, likely out of some military equipment.

[DMOD]

Al,

You might consider something like this (just a suggestion):