Kris Power Pump Upgrade/ Restoration

[loosecannon]

Hi All,

I havent been around here in quite a while, been hanging out at the CBT forum when time permitted, which hasnt been much!

Im getting back into doing projects and i recently scored an old beat up kris power pump linear amp.
it was cheap enough that it was worth it for the parts.

i have a thread going over at the other forum, but there's not much traffic over there, so i thought i'd start one over here so others can get in on the discussion.

this is my first tube amp build and im learning a lot about how these things tick.

yes, its a sweep tube amp. yes, the tubes are obsolete, expensive, and not meant for what they are doing...
we all know all of that already so please dont turn this thread into a debate about the merits of sweep tube amps.

the upgrades i am doing so far are:

1. adding parasitic suppressors. (lots of debate about this but i figured it cant hurt)

2. removing the driver tube and converting the amp to a straight three tube amp.

3. adding an input tuning network

4. i am adding 10 ohm resistors in series with the feeds to the cathodes as suggested in an ARRL article about sweep tube amps. its supposed to enhance the linearity.

5. i am adding bias to the control grid on pins 2 and 6 so the amp will be class AB1.

here are a few pics and there is a hand drawn schematic i made that shows the upgrades. its a PDF file.

PS- i forgot to mention my great appreciation to nomadradio who has been helping me along the way.

 

[loosecannon]

you will notice that there are no values on the caps and resistors in the voltage doubler circuit. this is because i dont know what values i want to use.
for the caps, i figure three 100uf 450v caps should do well as the plate voltage out is about 990 volts from what i read.
the resistors im not so sure about, can anyone lend some advice as to values and wattage ratings? i dont mind spending a bit more for parts that wont get so hot.

the other thing i need to know about is adding a disc cap in series with the input before the tuning network.
isnt it dangerous the way it is now?
what value should this cap be if it should be used?

im also looking at adding some .01uf caps and some resistors in parallel with the diode bridge, but need some specifics as to what to use.

thanks in advance for any and all input.

more pics to come!
LC

 

[unit_399]

LC -
Nice to see you back here again. I've been following your thread on CBT, and your amp restore is impressive to say the least. Back in the day, SBE made a 1 kw amp using 6LQ6/6JE6 sweep tubes. The amp was biased AB1, and the model # is SB-2LA. Here's a link to the service manual and schematic.

http://bama.edebris.com/download/sbe/sb2la/Sb2la.pdf

Maybe this will give you some ideas. 73s

- 399

 

[BJ radionut]

http://www.cbtricks.com/Amp/dentron/gla1000b/graphics/gla1000b_sch.pdf

Shows the parts and values your looking for also.
Dentron made a nice little sweep tube amp...
Diagram shows the tuned input values and good power supply/bias info...
Just a reminder this amp was made for SSB service...
Lots of info around on mods for this circuit, including changing it to a Russian GI-7BT tube (about $50 new for single tube) and about same output as the 3-4 6LQ6's

http://ko4nr.tripod.com/upgrades_and_modifications_for_d.htm

Good Luck
Welcome Back
All the Best
Gary

 

[loosecannon]

thanks for the replies guys.

will have a look at that manual 399 thanks!

BJ, i have definitely been using those mods and schematics for ideas.

more pics to come soon.
LC

 

[ExitThirteen]

I'll be watching this. Good to see you around, LC!


~Cheers~

 

[loosecannon]

thanks E13.

im really hoping to get an answer from some of you gurus on the value of a capacitor that i believe should get put in series with the input to the tuning network.
i think it should be .001uF, but i see a lot of .01uF being used.

im also wondering about what value/wattage rating of resistors to use in the voltage doubler circuit. i read somewhere that the 100K's will get too hot.

and anyone who wants to proof-read my schematic PDF please feel free.
any and all input is welcome.

ill be working on this over the next couple of days so i should have some more pics coming soon.
LC

 

[ExitThirteen]

Personally, I'd go .01uf 1kv for the series cap in the input tuning network. I think using a .001uf cap doesn't pass RF as well as a .01uf, and a .1uf would be too much (over-saturate). Will look into the schematics when I get time.

For the resistors, I'd go 220k 2W carbon film or metal oxide resistors. If you can get them, wouldn't hurt to go to the flameproof resistors. Just my .02.

~Cheers~

 

[loosecannon]

thanks again for all the replies.

i guess i will start with a .01uF cap in the input, but im wondering where exactly it gets placed.
right after the relay?
after the input tuning circuit?

the other thing i want to do is provide some surge protection.
i have read that when the amp is first turned on, the diode bridge is looking into a dead short until the caps in the doubler circuit get charged.

any ideas on how to help this?
is it actually needed?

im going to be putting some resistors and caps on the bridge diodes themselves also.
ill be using .01uf 1kv caps and 470k 1/2w resistors.

ill also be putting a .01uf cap in parallel with the primary of the transformer, and probably one on the secondary.

im open to any additions or suggestions to my plan.
LC

 

[ExitThirteen]

Personally, I'd install the series cap right after the relay.

You could perhaps take a Harbach soft start (made for the Heathkit SB-200/SB-220) and modify it to run in this amp, that may be the best way to limit inrush current strain on the caps and diodes.

~Cheers~

 

[loosecannon]

cool!

ill look into that.
LC

 

[loosecannon]

i looked at the harbach soft start, and i think i might make my own version. will look further into that.

the dentron GL-1000B schematic shows the caps after the input tuning section, and they use two .001uf caps in parallel.
i dont know enough to guess what the differences are, or why they chose to do it that way.

one thing im a bit concerned about is the current handling capability of RFC 5. (look at the PDF i attached to the end of my first post)

in the other amps that are already three final tubes, they are using one individual coil for each tube.

does anyone have any insight as to why i should or should not do the same thing?
im thinking one 100uH coil for each tube.

any input is appreciated.

ive got most of the board stripped, and once some big caps get here, im starting the assembly.
still need to find a place locally to test the tubes.

BJ radionut, i think we have a friend in common by the name of widowmaker here in Vegas. if thats true, then you might know of someone else here that has a tube tester?
just putting the feelers out there.

thanks to all!
LC

 

[ExitThirteen]

It would take a lot of current to burn out RFC 5, so I don't see a need to change it, but it certainly won't hurt anything to put a choke on each tube. However, I would check the value of RFC 5 and try to match accordingly.

My take on it, is that if you have enough current on the cathodes to potentially burn up RFC 5, you're most likely going to pop the cathode junction inside the tubes, and render the tubes completely useless in the process. You should never see that kind of current across the cathodes of the tubes unless you're putting a large amount of wattage into the amp, say something to the nature of 100W.

Just my .02 worth.

~Cheers~

 

[loosecannon]

thanks Exit13.

i was thinking that if i used three separate coils to ground, that i would have to triple the values like you would do with resistors, but looking at the schematic for the kris 600SSB, it looks like they do indeed use 100uH coils, so thats what i think ill do.

and as everyone probably guessed, i have more questions!!! yay...

again looking at the PDF schematic i posted, how important is RFC 2? its connected to the load cap.
other versions of kris amps dont have anything there. just curious.

something that concerns me is L1 in the upper left hand corner.
its in parallel with the filament of the bulb, and the meter shunt.
the problem is that its not actually there in my chassis. ( see pics)

wouldnt this mean that the entire RF signal coming out of the amp is running through the tiny filament of the bulb?
someone please set me straight on this, as im cornfused.
LC

 

[loosecannon]

ok, making some progress!

i answered my own question about the "L1" thing. it turns out that there is a wire about an inch or so long connected from one side of the lamp socket to the other.

its a coil with no coils in it! i would call this some sort of "gimmick" as can be found in other amps, but not really applied the same way.
either way, it alleviates my concerns about the whole amplified RF signal going through the filament of a lamp.

i have installed the new electrolytics in the voltage doubler, and i used 100k 5 watt resistors. open to input on this decision, but i think it will work ok.

i put a new power cord on it, and moved some things around to make room for the circuits im adding (bias and input tuning).
i used a ferrite snap-on bead and wrapped a few turns of the hot and neutral wires through it.
i also added a .01uF 1kv cap from the hot to the neutral wire.

i also started the input tuning section. the idea is to mount a 463 trimmer cap to the side and drill a hole so it can be accessed from outside the amp.

i have also done the bias wiring, and just need a couple of parts before its complete.

more to come...
LC