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Author Topic: What tube would you consider for this amp project?  (Read 27284 times)
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KM1H
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« Reply #25 on: August 01, 2010, 01:18:27 PM »

I suspect the downrating at 5KV was mostly to keep Charlie off their back.

Underloading any amp is known to create huge RF volatges in the tank circuit and even vacuum caps are not immune. Look at used glass ones, most have pecker tracks on the plates.

They also changed the original 3CX800A7 spec sheet after getting hollered at.

Carl
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Patrick J. / KD5OEI
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« Reply #26 on: August 01, 2010, 03:46:10 PM »

On the topic of picking tubes, assuming a cathode drive, is there any merit to deleting a cathode tuned circuit and putting a small halfwave rectifier tube across the K-Grid nodes so that it provides loading for the half of the cycle the RF tube's grid does not conduct?

Years ago there was a 3-1000 leenyar got in trade that had this arrangement using a 6AX4 (32V drop at 250mA) instead of a cathode tuned circuit. It worked great but I had no means to check anything on it back then and ended up selling it. The idea was to avoid the need for input tuning.
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Ralph W3GL
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« Reply #27 on: August 01, 2010, 06:14:04 PM »

        

          This "half cycle loading"  system has been used in high powered (50 KW+PEP)
          multiplexed ISB transmitters since the late 1950's. Most of the Airforce Globecom
          point to point Tx sites were packed full of them...        
  
           Eimac's Bill Eitel wrote it up in one of the ham rags back there some time as I recall.

           I user it with a couple band switched 4-400's back in the early 60's, worked fine...

           Ex AF 3034/3016...
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73,  Ralph  W3GL 

"Just because the microphone in front of you amplifies your voice around the world is no reason to think we have any more wisdom than we had when our voices could reach from one end of the bar to the other"     Ed Morrow
Steve - WB3HUZ
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« Reply #28 on: August 02, 2010, 09:46:37 AM »

No. You will just create more IMD.

On the topic of picking tubes, assuming a cathode drive, is there any merit to deleting a cathode tuned circuit and putting a small halfwave rectifier tube across the K-Grid nodes so that it provides loading for the half of the cycle the RF tube's grid does not conduct?

Years ago there was a 3-1000 leenyar got in trade that had this arrangement using a 6AX4 (32V drop at 250mA) instead of a cathode tuned circuit. It worked great but I had no means to check anything on it back then and ended up selling it. The idea was to avoid the need for input tuning.
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KM1H
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« Reply #29 on: August 02, 2010, 01:48:45 PM »

Maybe thats why some of those military signals sound like CBers Shocked

The concept might work better if there was some way to control the hard switch time to something a bit softer. Something like key clicks on CW Roll Eyes

Carl
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ke7trp
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« Reply #30 on: August 02, 2010, 01:57:52 PM »

Since we found some 4-1000s and sockets.  Should I use one or two tubes with this Transformer?  Should I do Grounded Grid or Grid driven?

C
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Ralph W3GL
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« Reply #31 on: August 02, 2010, 02:06:31 PM »

   


     No Carl, the military Tx output I'm talking about sounded like a hornets nest on
     the SP600/51j/r390/r390a in 16kc bandwidth at the audio output point (before
     the multiplex demod unit input)...

     They normally transmitted 32 incripted RTTY channels, 16 on each sideband...

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73,  Ralph  W3GL 

"Just because the microphone in front of you amplifies your voice around the world is no reason to think we have any more wisdom than we had when our voices could reach from one end of the bar to the other"     Ed Morrow
KM1H
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« Reply #32 on: August 02, 2010, 08:08:39 PM »

Since we found some 4-1000s and sockets.  Should I use one or two tubes with this Transformer?  Should I do Grounded Grid or Grid driven?

C

Yeah and now Im back to looking for them again since you changed your mind Grin  Anybody got plastic 4x1 sockets and chimneys?

Carl
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K6IC
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« Reply #33 on: August 02, 2010, 08:38:57 PM »

Clark,  Good news on finding 4-1000s and scokets.

Carl,  had posted this in the e-pay and links section of this site last week,  and appears this guy still has socket(s),  and chinmey(s).   Not at give-away prices but here is the link:

http://swap.qth.com/view_ad.php?counter=839173

Have been following this topic.  IF I had been starting from scratch,  I'd probably have strongly considered a 3CX3000A7.  They are pleantiful,  and a number of the sputtering amps have been floating around,  which are a good starting point for a HB Class 'A' amp,  wink  wink.  The 3X3 does require a bit of drive,  and the Vp max is 5 Kv ...  etc   Had also wondered about a 3CX/(X)2500A, altho not too available.

73  GL  Vic
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ke7trp
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« Reply #34 on: August 03, 2010, 12:40:52 AM »

I am concerned about a couple things here.  Just for learning sake can we talk about this?

I dont think I have enough PS for two tubes.  The transformer says 3650 0 3650 and 770kva on it.  Its for a BC rig doing carrier duty with two 4-400s.

I am also concerned that one 4-1000 will not put out nearly enough power if its Grounded Grid with 3000 to 4000 on the plate. 

My next thought is that if I do a Grid Driven setup with one tube, It might ok but still plate volts seem low for linear service here with SSB and AM amp.

What If I used this same Transformer in Full wave? That would get me more plate volts here.. I looked at the handbook and this is what I have determined.  Good choice?



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W1ATR
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« Reply #35 on: August 03, 2010, 08:38:15 AM »

Clark,  Good news on finding 4-1000s and scokets.

Carl,  had posted this in the e-pay and links section of this site last week,  and appears this guy still has socket(s),  and chinmey(s).   Not at give-away prices but here is the link:

http://swap.qth.com/view_ad.php?counter=839173

Have been following this topic.  IF I had been starting from scratch,  I'd probably have strongly considered a 3CX3000A7.  They are pleantiful,  and a number of the sputtering amps have been floating around,  which are a good starting point for a HB Class 'A' amp,  wink  wink.  The 3X3 does require a bit of drive,  and the Vp max is 5 Kv ...  etc   Had also wondered about a 3CX/(X)2500A, altho not too available.

73  GL  Vic

Another worthwhile thing to be said about the 3cx3000 is that with that enormous 4000W plate dissipation, short qsy's around the same band can be made without having to immediately jump on the knobs and get it retuned.
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WD8BIL
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« Reply #36 on: August 03, 2010, 09:25:03 AM »

What tube would I consider???

Anything with handles!
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K6IC
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« Reply #37 on: August 03, 2010, 12:39:08 PM »

Clark,

Think that your goal is to use this big PS to power a bigish linear amp.   The Kva rating you noted,  770 Kva,  cannot be correct.

If the transformer is from a 4-400 X 4-400 Plate Modulated rig,  then,  the transformer should be about 3.0 Kva.  Would expect it to be designed for a choke input filter,  in Full Wave configuration with the center tap grounded.  This should give you close to 3 KV output.  (I may be wrong on some of this,  as am not an expert).

So you need a tube which can give you good output power with approximately this output voltage.  Some  center-tapped transformers cannot survive being operated with their CT floating (as with FW Bridge config), as the insulation will break down,  and hurt the transformer.

Others more expert than I should chime in about now.

More later GL  Vic
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K1JJ
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« Reply #38 on: August 03, 2010, 03:05:23 PM »

I am concerned about a couple things here.  Just for learning sake can we talk about this?

I dont think I have enough PS for two tubes.  The transformer says 3650 0 3650 and 770kva on it.  Its for a BC rig doing carrier duty with two 4-400s.

I am also concerned that one 4-1000 will not put out nearly enough power if its Grounded Grid with 3000 to 4000 on the plate.  

My next thought is that if I do a Grid Driven setup with one tube, It might ok but still plate volts seem low for linear service here with SSB and AM amp.

What If I used this same Transformer in Full wave? That would get me more plate volts here.. I looked at the handbook and this is what I have determined.  Good choice?


Clark,

That transformer should be fine producing around ~3600V or so in the  full wave center tapped mode using a choke input. You should put a vacuum relay across the choke (short it out) to get a voltage boost near 4KV or so under load. Also, if there are taps on the primary, use a high current relay to add some more boost when desired.  You will be able to stay away from a Variac this way and see better regulation. . The sag will depend on your filter cap size  (at least 40 uf) and the load.  Put a good pair of 4X1's in GG and you will get out about 3500 to 4KW pep into a dummy load. This is a good, conservative set of parameters for all components and the amp will run clean and efficient if you find the correct tank values and use a tuned cathode input.

I'm not a fan of grid driven 4X1's in linear service  due to the added circuit complications and lack of negative feedback - that is free in GG config. (also more stable in GG)

T
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« Reply #39 on: August 03, 2010, 09:13:29 PM »

Swamped grid driven solves neutralization and a lot of parasitic problems but 4x1's still require a good layout to be stable.

Carl
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ke7trp
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« Reply #40 on: August 04, 2010, 07:34:38 PM »

I will go read it again. Its the sale electro-engineering unit that where in thousand sof 20V's, 707s, gates ect...

I have the PS done. I hooked the old RF deck up to it one night and put a 1kw Carrier in the dummy with it.   I had the variac at 3000 volts.  My brother walked in and like an A-hole said what would happen if I did this.. Then cranked the variac up to the max. It was around 5K volts.  That was the boost of the Variac on my high line voltage.

So 4-1000 in  Grid driven needs move voltage.




C
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Detroit47
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« Reply #41 on: August 14, 2010, 05:08:34 PM »

I've built several amp's with 4-1000's. Both grid driven and GG I have had good results swamping the grid using 100 watts drive. Here is a reprint from 1963 QST.

* 1.pdf (287.61 KB - downloaded 409 times.)
* 2.pdf (138.27 KB - downloaded 358 times.)
* 3.pdf (100.45 KB - downloaded 413 times.)
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Detroit47
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« Reply #42 on: August 14, 2010, 05:14:03 PM »

I've built several amp's with 4-1000's. Both grid driven and GG I have had good results swamping the grid using 100 watts drive. Here is a reprint from 1963 QST.

Here is the rest of the PDF

* 4.pdf (129.64 KB - downloaded 373 times.)
* 5.pdf (274.6 KB - downloaded 348 times.)
* 6.pdf (42.12 KB - downloaded 363 times.)
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Patrick J. / KD5OEI
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« Reply #43 on: August 14, 2010, 07:46:03 PM »

Thank you! I love good articels like that.
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