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Author Topic: 815's as modulators  (Read 10362 times)
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WZ1M
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« on: October 22, 2009, 12:22:05 PM »

I have a pair of nos 815's kicking around and thought it mite be different to use them as modulators for a pair of 813's. Doing them in push pull parallel. Whats your thoughts?
Regards,
Gary...WZ1M
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KE6DF
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« Reply #1 on: October 22, 2009, 12:26:56 PM »

There are articles for using 815's as modulators in the old handbooks.

The problem is that from a single 815 you get around 50w,

So a pair would put out 100w - 110w, but that's not enough for a pair of 813s unless you run the 813s way below potential.
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KM1H
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« Reply #2 on: October 22, 2009, 01:02:24 PM »

That was one of my favorite tubes back then, I built several items around it from audio to 6M.  QST and CQ used them a lot for audio and RF articles. A pair would be fine for a 4D32, 6146's, and similar and have a lot of reserve.  Or a QRP 813 Grin

Carl
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The Slab Bacon
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« Reply #3 on: October 22, 2009, 01:05:25 PM »

Gary,
       An 815 is basically a pair of 2E26s in one bottle. One will do 50-55w out at 500v on the plates. So they would be a bit small for a pair of 813s. One other problem is to get full strap out of them, they want to be run AB2, so you have to tickle them with a little grid current on the peaks. This means you have to have a driver circuit that can shove them into grid current. (transformer coupling or cathode followers). With the varying input impedance, you will also need to wrap some feedback around them as well. (I am using a pair of 2E26s for the screen modulators in my 4-1000 rig)


                                                       The Slab Bacon
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N2DTS
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« Reply #4 on: October 22, 2009, 02:05:54 PM »

Might be fun to try six water cooled 6aq5's in push pull tripple....

Maybe run them at 2000 volts imersed in liquid nitrogen....

Brett
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WB6NVH
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« Reply #5 on: October 22, 2009, 05:39:41 PM »

I have a commercially made "mystery" mobile transmitter from the late 1940's which uses one 815 as the modulator and a second as the PA.  Modulator 815 is P-P of course, and the PA is parallel configured.  An odd choice of tube I would think, but they were probably common after WWII and cheaper than a set of 2E26's.  As I recall, the navy ATD transmitter used the 815 (or was it the GF...)

EDIT: In response to the question about a photo, it's on my "Mystery Radios" page on my website, second one down, labeled the "N1-DC Transmitter"

http://www.wb6nvh.com/mystry/mystry.htm

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Geoff Fors
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WQ9E
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« Reply #6 on: October 22, 2009, 05:56:50 PM »

I have an almost finished homebrew 815 modulator that came with my Lysco 600.  It is built into a blank grey National case (small receiver sized) and has the parts for the modulator and a 2" scope tube.  Completing this to go with the Lysco is on my very long to do list but for now the Lysco is used CW only with an RME-99.

The 815 tubes are still common at hamfests and I picked up a couple of spares just in case.

Rodger WQ9E
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Rodger WQ9E
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Patrick J. / KD5OEI
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« Reply #7 on: October 22, 2009, 08:01:12 PM »

Was not the 815 the predecessor of the 829? I have a few of those, they take the 7-pin sepatar socket.
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KM1H
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« Reply #8 on: October 22, 2009, 08:13:58 PM »

It started with the 832 in 39 or 38, then the 815 and 829. Tube Lore has wrong dates for all 3.

Carl
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W2PFY
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« Reply #9 on: October 22, 2009, 08:59:08 PM »

Quote
I have a commercially made "mystery" mobile transmitter from the late 1940's which uses one 815 as the modulator and a second as the PA.

Is there any chance of a photo of it?
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The Slab Bacon
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« Reply #10 on: October 23, 2009, 07:30:42 AM »

It started with the 832 in 39 or 38, then the 815 and 829. Tube Lore has wrong dates for all 3.
Carl
KM1H

dont forget the 5894 and the 8643  Grin  Although they were designed more for VHF service. But then so was the 832, and 829B.
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KM1H
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« Reply #11 on: October 23, 2009, 12:41:36 PM »

There were several post WW2 improvements. The 1952 Amperex AX9903 was the son of the 829B/3E29 and daddy of the 5894 and the 7854 was a bit bigger. The 6524 was the 832A upgrade. And Motorola had a bunch of their own numbers to con users into buying from them.

I use a modified Hallicrafters HA-6 on 6M and the 5894 runs a very clean -34 dB IMD 3rd which is 1dB better than the converted NCL-2000 1200W amp.

Carl
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The Slab Bacon
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« Reply #12 on: October 23, 2009, 01:17:35 PM »

I cant remember what it was, but I have the modulator deck out of a piece of VHF-AM gear, I think it might have beem military that used a single 829B push-pull as a modulator. It used a rather interesting 3 terminal autotransformer for the mod tranny.

I have been pondering using that autotransfoma with a P-P 815 in my Glob Scrote 680. The octal 815 would require just 1 octal socket. This way I could eliminate the 6L6 Heising circuit and not have to butcher up the chassis with another large hole.
Since I will not need the 50w the tube will make, I might be able to get away with running it AB1 instead of AB2 that it needs for full outpoot.

                                                        The Slab Bacon 
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W9GT
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« Reply #13 on: October 23, 2009, 02:12:29 PM »

Interesting discussion.  I built a six meter transverter from a magazine article back in the 60's that used an 815.  Great little tube.  That little transverter was simple, but it worked and made 20 watts or so on 6.

Recently, I acquired an old buzzard AM rig, built in a short rack cabinet that uses an 829B in the final, plate modulated by an 815. Probably built right after WWII or in the late 40's.   It uses all plug-in coils and is really a beautiful home brew job.  It is presently set-up for 10 meters, but plug -in a few different coils that I already have and possibly add some padding capacitors and it could be on 75 or even 160.  It is quite large, however, for a rig that probably would have a problem making 100 watts out.  Probably, more like 75-80 watts at best.  Anyway, it was given to me and I really want to get it on the air and just preserve a nice bit of history.  It is full of meters and very well-constructed.

As for 5894s....yeah great tube!  Used in GE MastR Prog line xmtrs among others.  Kinda like a heavy duty 829B, although rated at 90 watts out on 2M.
They used to be quite expensive, but now pretty common at cheap prices.  829Bs are still also very common and readily available cheap.  815s seem a little less common, but still around.  832s are baby brother of the 829B and they are also still quite common, but only good for about a third of the power.

All very good tubes for projects that might be a little more interesting and unusual as compared to the common 6L6, 807, 2E26, 6146 stuff.

73,  Jack, W9GT

 
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73, Jack, W9GT
KM1H
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« Reply #14 on: October 23, 2009, 06:38:56 PM »

If you mean the 6M TX converter that used a 6J6 oscillator and the 815 as a mixer I built that right after the article came out and wow was it dirty. Luckily I had access to a spectrum analyzer at National before putting on the air and built a bandpass filter. That ran barefoot for a few months into a 6el yagi up 90' and 6' above a TH-6DX and did rather well. Then I converted a NCL-2000 engr prototype to 6M and really got out. That converter is out in the storage trailer and I still use the NCL-2000 with the HA-6 transverter.

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WU2D
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« Reply #15 on: October 23, 2009, 07:32:21 PM »

A long time ago I dropped the socket on my SCR-522 TX with spacers. Thus converting it from an 832 final to an 829B. About 25W out. Nice upgrade and the 6V6 modulators actually work because they modulate the driver as well as the finals in that rig. Very clever setup in that radio.

This was a joke picture with the rabbit ears!

Mike WU2D


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