805! Woo Hoo!

[VE3GZB]

I've just been from my friend's place, he gave me a nice 805 for my homebrew rig!!

[VE3GZB]

What I think I'll do then, since I can't plate-modulate at this time, I'll grid modulate it. I'll run it lightly from the 950VDC supply or if that's not good, I'll use the 800VDC supply.

Then later on if/when I get a plate mod Xformer, I can look at using the 1625s to plate modulate it.

This will be a big redesign on my part but fortunately I have most of the hardware on hand. I don't have sockets but I have a good Weller soldering gun and I know how to use it!

73s
geo
VE3GZB

[N3DRB The Derb]

805 is a bitch-en modulator tube. I imagine it would do some decent rf too but the leads on that bad boy are really long. I'll look for a good neutro cap for you at the hamfester tomorrow. also a 805 socket or 2.

at 1500 volts they (2) needed -22 bias for keeping the static plate current down to around
90 mils. I could pin the 0-500ma current meter, although thats not a good idea. 

I think you should use 2 of them for modulator service and one of us will snag you a final.

I am biased toward eimacs if you must do other than triodes. pair of 4-65's are cheap and will do well, under high voltage lower current conditions.

[W2PFY]

I think you would be a lot better off if you used those 1625's as a cathode modulator than try to grid modulate it. Fir starters you would get hi fi sounding rig and more output than with grid modulation. If I remember correctly with grid mod you need to have very precise settings to get it to sound good. You will need no iron with cathode mod with the exception, possibility of a 10 Henry choke in series with the center tap of the 805 filament transformer for monkey swing to the plate caps of the 1625's. Come to think of it, you didn't ask for this so it's just my 3 cents worth  

There are other people on here that have used cathode modulation. you could still plate mod it if you have an audio output transformer and a hi fi amp to supply the audio. Lots of ways to do it.

[VE3GZB]

I'll look for a good neutro cap for you at the hamfester tomorrow. also a 805 socket or 2.

Thanks! Yea, I don't have a socket and any caps I have are much lower voltage than I should risk....I could fabricate a cap but because of the high voltage, any insulation would have to be air, so it wouldn't be very stable.

I did look at this old military Xtal RX I snagged at the Fergus Hamfest....I scavenged a bunch of receiving tubes (6SK7 and their ilk), some octal Ceramic sockets and some small varicaps too! Nice!!

If you come across 7 pin sockets (as cheap as possible of course) for the 1625, I'd appreciate it because I have none and to use them I'd be soldering to the tube pins. I can swap you some of these nice Ceramic octal sockets and varicaps if you like!

Thanks!
73s
geo
VE3GZB

[VE3GZB]

For my mic, I took an old junk CB mike I picked up cheap somewhere and changed the broken carbon element for a Xtal piece, salvaged from a piezo buzzer. Siliconed it in.

I'm using a pair of 6AU6s for my speech voltage amplification and when it's terminated into 47k||22nF I get a very good looking speech signal on my scope, 120Vp-p.

[W2PFY]

Another option would be to find an 803 and just screen modulate the 803 with the single 805.

You would use a 100 watt plate dissipation 805 tube to modulate a screen on a 803?

[W2PFY]

My point is the 805 is a better tube for audio than it is for RF

I agree and it would be fun to use it as a cathode modulator or it could be run in class A plate modulator with higher voltage on the 805 hysing connected. Well enough from me, don't want to confuse the builder.

[WBear2GCR]

The 805 and its cousin the 838 are FB modulator tubes.
Best saved and used for that purpose.

They run "zero bias" in Class B as a modulator. Not good for a SE modulator, imho. For that you want an 845 or 211 - Class A "zero bias" tubes. Chinese versions will work FB.

I think PFY is giving you good advice - 1625s or 807s are rugged and plentiful, inexpensive. A quartet of them set up for AB2 will have an output power of 200 watts, fyi. You use a slightly high plate voltage, but they don't mind in modulator service. The also work FB as RF tubes. The ARC-5 ran two of them... W2JBL can be heard on the air with a modified ARC-5 on many nights here on the upper east coast sounding berry gud.

The cathode modulated idea is not half bad here either... because the voltages are fairly low (imho).

I think there are two ways to build up something - assuming you want to build up something and not just buy a DX-100, Apache or Johnson rig (for example). First decide on the power level and buy parts to suit. Or, alternately, second find whatever you can and fill in the blanks to suit.

The two main things are going to be IRON and Toobes, that and RF parts. That kinda dictates the direction...  so as I suggested you can either build to a plan and get stuff together over time, or you can find stuff and build what it permits... it's hard to work the two methods together.

For example, an op here in upstate NY has been getting parts together for 3 years to build up a plate modulated transmitter based on a particular large tube... (building to a plan).

Otoh, you might find an RF deck or modulator at a hamfest, or online and then build to that, because you can... 

As someone mentioned, 6146s are still inexpensive usually, and 807s, 1625s are also inexpensive, as are import 6550s (modulator tubes) and 6CA7s... for that matter so are 4D32s not too pricey for the time being... etc...

I'd say KISS - (keep it simple) and aim for what you can put together, and don't be in a hurry to use something just because it dropped into your lap, unless you end up finding the "rest" of the things needed without going crazy... sometimes it makes sense to resell things that are "desireable" for things that you can really make use of...

Now, if you had a few boxes of NOS 805s... more options open up. But one? Not so sure you want to go ahead and do much with one.

Ymmv.

                    _-_-WBear2GCR

[W3SLK]

Brian said:

The 805 is a great tube, but VERY hard to find.

That's because I cornered the market on them, 813's and 810's years ago, hah, hah!!  The plate in the 805 is the same as in the 810. Very stout. I use a pair for the modulator to the MK-214D and the ET-4336F.