The AM Forum

These are the candidates for the Tuning and Loading caps for the new HB rig. not doing a swinging link like last time. the coils are too hard to come by in good shape.

Regular old Pi-net this time. The tuning cap is a Hammarlund TCD-240J, which I cant find any info on. Hoping one of you guys have more info for me as to voltage rating - I assume it's a 240pf max per section. It's a huge bread slicer. I'd rather it be too big than too small. when I know the voltage rating, I can start figuring out how much plate voltage I can run - n start figuring out what RF tubes I can run - and what plate transformer/chokes I need to get.

Vertical size is a issue as this is only a 36" rack. Tall tubes like the 813 might be a problem. Besides that, I am getting bad vibes that the 813 might be the next big tube craze in the audiophool world.  :P

the "little caps " are the load caps, the silver one is a maximum 1540pf, and the brass one is a maximum 2160pf. the brass one is a bit nicer cap IMO.

I'd like to be able to run a 300+++ watt carrier.

Thanks for any info on the hammarlund. General thoughts on my thinking processes invited.

You don't need a spec sheet for the voltage rating.  All you need to know is the plate spacing and apply your favorite fudge factor.

As a very recent data point, I just replaced a 1/8" spacing air variable with a 7kv vacuum job on my 8000's rig because of too frequent breakdown at 2kv DC.

It not only sparked with modulation peaks but even when I unkeyed.

Big bread slicers are hard to come by and terribly expensive these days but vac variables are readily available but not exactly a dime a dozen either.

js

Generally, .120" spacing is rated for 4kv

Some leading manufacturers  rated .25"  at 9kv.

I have some Palstar 5.5kv caps here they are rated for 5.5kv...
I'll get one out of the box later and measure the spacing....


Bread slicers are still around, but you don't see them at the prices you wish you could.

There are manufacturers, such as Orrin Elliot (in Ohio), that will make whatever you want. But, they cost about as much as a vac variable.
(they make the "M73" caps that Surplussales, RF Parts and MFJ sell... it's their "bottom of the line" product)


I've settled on paying $140 each for brand new, 550pf,  5.5kv caps from Palstar..

Derb,

From the 1939 ARRL handbook catalog section, page 484:

TCD is split-stator type (individual sections) good for push-pull operation
up to 1 KW

TCD-240J 250 pf. J suffix is 0.100" spacing, 4250 V.  11 1/16" overall length.
$19.00

Other suffix spacings and ratings:
F 0.171" 6000 V
J 0.100" 4250 V
K 0.084 3750 V
L 0.070" 2000 V.

129 at RF Parts.

And PalStar rates .125 spacing at 6 kV!


--Shane

A shunt feed like a pi-net doesnt require the same spacing as a series feed.

Ive had no arcs with 4.5kv spacing ( SB-221 or wide spaced replacement for SB-220) and 2.5kv B+. Its a standard OEP size at 250pf.

Arcing on unkeying sounds like parasitics or poor neutralization.

Carl
KM1H

thanks Tom for the good dope OM.  :D

Yup, but RFparts charges TRIPLE the shipping!

(They like to charge for their time packing etc...)
They charged me $17.00 to ship me 2 transistors!

Ends up costing the same as direct from Palstar.

The Palstar c600 (5.5kv) is about .140" between plates.

That's not shipping, that's the "handling" charge.  I NEVER could understand how a company could justify handling charges....  I mean, do the math, the guy packin that stuff ain't makin what we, the customer, is payin...  That's a HUGE profit center!

1    25-350   45    0.125    6 kV    3.8" x 3.8" x 9.3"    115.00

That's the 350-6KV, where I took my spec from...  I'd believe you, tho, since you have an actual one in front of you, rather than a spec sheet...  Learned long ago that spec sheets aren't updated NEARLY as much as actual parts are!

--Shane

Derb,
I use the same large cap in my 160 meter class E rig output tuning. I think it is 640pf total. It never flashes at 1500 pep AM over 150% PP. a bit large for a plate tuning cap. I had it as a loading cap in the 4CX3000A with a dork knob padder on 75 till the padder changed into an M80. 

You're correct Tim,
The 813 is a great audiophool tube for those looking for a 1KW audio amp. Four of dem in push-pull parallel and 2500V on the plates.
I chime in on the "Audiokarma" forum and I can always pick up on the usual sayings these folks use and their acronyms.

Fred

Sounds like the time to start gathering the 813's into the AM fold...

Also, time for a 'disinformation' campain.

klc

yeah, it seems the 813 is about to become "the next great tube" in that world. Lotsa buzz going on.

Ive been signed on to Audiokarma for a few years and toss a zinger in once in awhile and then watch the fun. 8)

Maybe a thread about the 813's secondary emission causing distortion and smoked transformers needs to gather some momentum.

Carl
KM1H

must be ICAS PEP.

must be ICAS PEP.
[/quote]

Yeah, that's what I thought.  :)

Taken directly from Palstar's spec sheet on RFParts.com.

--Shane

a pity because Palstar is supposed to be one of the best ones and is certainly expensive.

What is ICAS PEP as it relates to breakdown voltage?



Yeah, that's what I thought.  :)

Taken directly from Palstar's spec sheet on RFParts.com.

--Shane

[/quote]

A sorry attempt at tongue in cheek humor....  About as much as the spacing and rating they gave that cap! :)


--Shane

Roger that. I was wondering since the peak voltages across the cap would be the same for CCS or ICAS.

There are too many good bread slicers available at hamfest to waste money buying them from Rip Sales of Nebraska or RF Parts.

I wonder if they meant Dosy Volts.......

Hrm....

--Shane

LOL.  ;D

Good old Dosey.

wow. those things are massive.  :o