TEN TEC AMP

[W8UJX]

I'm rebuilding the power supply in my Ten Tec Centurion amp.
The circuit uses 20 ea 1KV diodes and eight 220 uf, 450 VDC caps in series in a full wave brige circuit.

I see caps ranging in price from $2 to $10 each on Ebay.  I have no experience with these caps.  My question is which caps are ok and which caps should I stay away from.

Any advice is appreciated.

Thanks,
Jerry, W8UJX since 1954   

[Pete, WA2CWA]

Do you need axial or radial? Mouser probably would be a more reliable source for "fresh" capacitors then ebay. Get caps with a higher temp. coefficient rating. Not a part to skimp on price especially in a linear.

[N4LTA]

Buy some good name brand low ESR caps from Mouser or Newark. They are less than $10 each in 10 quantity.

Get something like Nichicon or United Chemicon or Cornell Dublier. I just looked at Mouser and they have some low ESR scap for around $6 in tens. I'd stay away from EBAY and buy new stuff from a reputable dealer.

Pat
N4LTA

[WQ9E]

Go with Mouser and also go with 105 C caps instead of the lower cost 85 degree units.

[N8ETQ]

Hey Jerry,

   You may want to look at this guy.

http://www.wjoe.com/capacitors.htm

  I made up a 10uF 4Kv bathtub for an HT33B using 10
100Uf Radials @ 400V. Good price for 105C Nichicon's.
Fast ship too.

/Dan

[W8UJX]

Thanks Dan,

That's exactly what I need.  As usual, you guys came through again.

Jerry, W8UJX since 1954

[K5UJ]

If you want to use the amp for AM, you might consider thinking outside the box (literally).

It depends on whether or not you want to keep the amp looking stock and pretty in case you ever want to sell it (and keep the Ten Tec nuts happy).

If you don't care about that and never plan to have a real AM rig (Viking 500, GK500, BC610 etc. i.e. a 500 watt or more rig), then I'd build the amp out to the sides either on a table or in a rack on a shelf.  The table top idea is only good if you have a shack you can restrict access to, so you don't have to worry about pets and kiddies getting in there.

Take the top cover off and saw off the sides, or keep it and use some other sheet metal.  replace the stock fan with one of similar size but  moving twice as much air.  You may have to go for a DC fan powered by an external supply.  With the other side off, you can pull out the dinky stock plate iron (which lightens up the amp making it a lot easier to work on) and run something giving you an amp or two CCS out to the side.  At this point, you can also get a few oil caps, 2 or 3 each 15 uF 5KV and parallel them with bleeders and your cap problem is solved forever.  Replace those wimpy disc ceramic caps in the tank circuit with HEC doorknobs.  Now you'll have an amp that will sit there and put out 300 or more watts AM for as long as you want to transmit.

rob

[KM1H]

ALWAYS look at the date codes on electrolytics. Up to about 10 years on a quality name brand cap is pretty safe but you should reform first while monitoring leakage. Im using a bank of 2001 470uf 500V Mallory's that I got real cheap for one of the HB amps ; they were removed from never used equipment. Using just an old Oregon variable DC bench supply and a VOM with switchable current positions they formed quickly to well under 100 microamps leakage.

For customer repairs I buy new computer grade from Ameritron/MFJ or CDE 381LX series 105*C Snap-Ins from Mouser. For my own stuff Im a cheap SOB

Always check tolerance of the equalizer resistors in any commercial amp, some may be way off depending upon type and quality used.

Carl

[W8UJX]

I want to keep this amp as stock as possible. 

For now I will build an outboard power supply using a Thordarson power transformer #T19P63 and five 4uf, 4KV oil filled caps I found in the tool shed.  The transformer secondary is center tapped 2500V and 3100V at 500 mA.  I will use strings of the 6A10 diodes with the 2500 volt taps in a full wave bridge circuit similar to the amp.

I already have a GK500 that I use on AM.

I will have to drop a hint to the XYL that a rewound transformer would make an excellent Xmas gift.

Rob - Can you give me a part number for the HEC doorknob cap and more info (mfg and part number) for a better similar size fan. 

I built a 300 watt modulator using a pair of 813’s connected in triode configuration driven by a Heathkit 20 watt amp.  I may try to high level plate modulate the amp at a later date. 

Jerry, W8UJX since 1954         

[K5UJ]

I used HEC doorknobs.  I bought mine from RF Parts.  The part numbers were 580300-7 580170-7 and 580400-7

They are HEC HT50s 7.5 KW for 170, 300 and 400 pF. TC is N-750 and N-3300.  Check the Centurion schematic but I think the 400 is used on 80 m., the 300 on 40.  There is an unused lug on the bandswitch that is connected when the switch is on the 160 m. position.   I may have it backwards and the 170 is on 40, 300 on 80 and the 400 on 160. Whatever corresponds to the stock values go with that and the one left over is for 160.  I believe (this was a few years ago) I snaked a lead down from the switch to the bottom of the cabinet where the caps are positioned and added a cap for 160 because on that band you can run out of loading C.   There may have been changes over the production run and your amp may be different.  You'll have to get in there under the tune air variable and remove those disc caps and their terminal lug and fashion a copper L strip with a hole in it for the chassis ground screw and bolt your caps to it and put lugs on the bandswitch leads and bolt them to the other ends of the doorknobs.  It is probably easier to make extensions with lugs on them and solder them to the bandswitch leads.  I didn't want the hassle of removing the tune cap but of course if you do that everything is much easier.  You might consider removing the disc ceramic blocking caps and putting in a pair of HEC HH58s, 1000 pF TC X5V also 7.5 KV.  These are all listed here:
  http://www.rfparts.com/caps_ceramicdoor.html

If you don't want to spend money on the HECs you can perhaps use Russian doorknobs from QROparts on eBay.  I had tried a bunch of different caps including big micas from hamfests and was tired of fooling around.  The total for all the HECs I bought was around $100.
You might also find some deals on used CRLs on eBay but make sure they are Class II RF doorknobs.

The fan I used came from Digi-Key.
http://www.digikey.com/product-detail/en/4715SL-04W-B69-D00/P13427-ND/857920

It is important to follow the cooling path through the power supply and out through the RF deck.  But on AM when the tubes are dissipating 700 or 800 watts dead carrier the stock fan doesn't get it done.  This fan consumes 23 w. so you need a fairly big 12 v. ps for it.  There's no free lunch--when it spins up you'll think you are running a TV transmitter and may decide your Globe King is pretty good after all.

If I had not already had all this gear on hand I would not have bothered with these mods and am working toward getting a vintage plate modulated rig on the air.

73

rob

[W8UJX]

Thanks Rob,

I did not know the amp used some fixed loading caps until you mentioned them.

My amp uses both caps, 430 and 330 mic on 160 and 80 and just the 330 mic on 40.

Right now I use the amp on CW only.  It has been working great for the past 20 years until the power transformer blew a few weeks ago so I will probably hold off on any mods unless I want to plate modulate the amp later.

Jerry, W8UJX since 1954

[Rob K2CU]

You will find that the radial lead (aka Snap In) caps a quite less expensive as ther eis higher production of them. If your old caps were axial leads, try  to match the diameter, especially if there is a body clip to hold them. So, you have to add leads...big deal. Also look for parts with the highest design service life. These caps come in 1000, 2000, and 3000 hour ratings. Obviously go for the longer life and higher temp parts.  And, don't be cheap, just thrifty.

And, unless unobtanium, only buy new for a reputable supplier, never old stock.