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Kris Boomer Tube Convertion Help

T

T23

Active Member
Apr 17, 2010
645
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Hello, I am thinking of eventually trying to convert a Kris Boomer sweep tube amplifier to a currently in production tube, I see that the EL509 will work, but they stopped making the ones with the plate caps in 2008 and all there is now is NOS. They also have an octal version still in production that will work too, but I have some questions...

I would like to know if the coil on the plate cap clips is still necessary if the plate connection is in the base of the tube as with the octal version of the el509 or not?

Also I was looking at 6146 tubes as-well.

As you can see in the schematic the amp has a 120 volts dc on the plate and a 6.3 volt filament. The current 6JU6 tubes draw 3.2 amps together, but I don't know what the power transformer is capable of.

Could anyone suggest any other tubes that are currently in production that may work?

Any other comments welcomed also...

http://www.cbtricks.com/Amp/kris/boomer/graphics/kris_boomer_sch.jpg

T23
 
Last edited:

Ok. I see now. That helps. Any suggestions as to a tube? Is the coil needed?

Also there is another spot for a third tube socket...


T23
 
Anyone see what's wrong with that circuit?
It's suppoed to be a grounded grid circuit but in transmitt where is the kathode going when switched over to driving radio?
If you have no RF circuit knowledge, leave it alone.
The original designer hardly knew what he was doing!
 
KM3F said:
Anyone see what's wrong with that circuit?
It's suppoed to be a grounded grid circuit but in transmitt where is the kathode going when switched over to driving radio?
If you have no RF circuit knowledge, leave it alone.
The original designer hardly knew what he was doing!
Click to expand...


The cathode goes through RL1B directly to the transceiver jack on transmit as it should. A tuned circuit would have been nice however. The only thing I see wrong is the tail from RL1B to RL1A which I don't really like as it is too close to the output and makes for easy feedback and oscillations.
 
Ok, so would anyone have have any idea what tubes I could use then to convert this amp? As I said I am not doing this immediately, just wanted to convert this this amp to a tube that's in current production.

My ideas:

The KT88, has 42 watts of plate dissipation.

Or the octal el509.

Now with either, do I need to keep the inductor on the plate tube caps or not?

T23
 
Thanks 399. Strait and to the point...

Now I am leaning towards the el509 octal type tube, but what about the kt88?

Tubes like the 813, gu13, 811a, 572 would require more plate voltage, correct?


T23
 
That schematic doesn't look right to me either. There is no DC return path for the tube cathodes as shown in the schematic. Are they assuming there is going to be a DC choke on the exciter output to bias the tubes on? If so, that's a lot of bias for those tubes. There should be some stable negative voltage on those cathodes to keep the tube from over dissipating.

If there is room for a single 811A, I would consider this first since your B+ supply looks easy to step up and the 6.3 volt filament will match. Get rid of the full wave bridge and replace it with a voltage doubler. Then there will be ample plate voltage to run the 811A.

Of course that still leaves the bias issue in the open and more complex with the directly heated cathode of the 811A. It will need a filament choke and bias applied from a zener or zener and transistor combo. There is no center tap on the filament winding to make this easy so you'll have to use another filament transformer or another trick is to parallel a transformer with a center tap to the existing one.

The tubes you mention without anode caps are geared towards the audio amp guys. By terminating the anode connection in the base socket, we increase the stray capacitance between the input and output of the tube. Not a big deal at AF frequencies but something to consider at RF since it increases the chances of self oscillation.

Many audio tubes like the 6L6, 6BQ5, and 8417 have been placed in RF amplifier service with good results in the HF spectrum so it is an option. Stay away from newer 6146's because they just don't hold up like the old ones. They also have lower plate dissipation then many large sweep tubes.

Not a lot of good choice left for smaller triode amps. The EL-509 was promising and showed very strong peak emissions on the tests I made. Don't judge a book by the cover though. Further testing showed later EL-509's could be easily stripped of their oxide coating on the cathode by over driving and they had severe issues with the filament pins cracking the glass envelope because they were conducting too much heat. I'm not surprised they have been discontinued.
 
Just an idea, kinda thinking out loud. But depending on room. There are some russian coaxial NOS tubes that can be had very cheaply. I think a GI15B is one if I remember correctly. Only requires 1000V on plate. It is a coaxial base like larger triodes with metal anode heatsink. Filament is 12.6V. Just need a fan to blow thru. I think Chris at nomad is doing something like this with a lot of the old sweep tube amps and putting something like a GI6B in them. The tubes are NOS but can be had for around $15 each. I just bought 14 to have on the shelf. The 6B, max plate V is 2500V @ .175mA. Filament is 12.6V @ 2A roughly. With a plate dissipation of 350W. There are smaller cheaper versions like the GI15b or 13B that can be had for like $10 or so. Maybe a little more work than you like, but I thought I'd throw it out there.
 
The only issue with the Russian radar tubes is gas inside the envelope that greatly increases the chances of an internal tube arc. I can't speak for the GI-15B specifically but the GI-7B has a high failure rate unless the tubes are conditioned first.
 
Thanks guys for the usable info, I think I can work with this. What about the sockets for these Russian doorknobs?

T23
 
Sockets for the GI7BT...are not required (perse') they can be mounted straight on the chassis....
Most of the "GI" coaxial series can be mounted that way.
I however prefer a socket on the GI/GS series so that the tube is removable without unwiring the filaments...etc...

I don't think KA4POZ still has GI7 sockets anymore....
Last I got were from a VE3 that sells only on Ebay...just search GI7B sockets there....
Very nice sockets! expensive $50 each...but well worth the cost in my book...
He custom makes other GI/GS sockets also...He does excellent work IMHO...

I get my GI7's tubes from only a couple sources QRO-Stuff or QRO-Tubes...cost a little more $37 vs $20-30....but they test before ship...again just me...
Also there are (2) versions of that tube...GI7B(std)....GI7BT (H/D Mil. radar spec)...BT's have much lower failure rate if conditioned correctly before usage
GL
All the Best
BJ
 

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