[Amps] 572B AMP PLANS

[Jim Thomson]

Date: Sun, 26 Dec 2010 22:06:08 -0600
From: "Jeff Blaine" <keepwalking188 at yahoo.com>
Subject: Re: [Amps] 572B AMP PLANS
To: "Hsu" <hsu4qro at gmail.com>, <amps at contesting.com>
Message-ID: <0FB28AAD039F4D3B93D503C58EB78222 at 8710w>
Content-Type: text/plain; charset="iso-8859-1"

Hsu,

The 813 looks nice.  But I am very impressed with the GI7B.  I really work that tube hard - both in the RTTY contesting and on the 
bench (one time, I ran the pair for 20 minutes key down at rated power) for simple endurance test on the amp.  Finally had to stop 
out of worry the DL was going to explode.  hi hi.

If I am needing to use glass, I think I prefer the 3500Z if you have high enough plate voltage available.  I'm not sure what the 
3-500z looks like at 2500V.

Good luck!

73, Jeff AC?C
www.ac0c.com

##  I have  4 x Drake L4B's.... and the no load is 2650 vdc on RX... and with 800ma cxr... the B+ drops down to 2490 vd.   Since
I added a 50 ohm-50W WW glitch R in series with the B+,  I lose another 40 vdc  across the glitch R.   The pair  of 3-500Z's  just
last  a Looong time.   IMD is superb. 

##  IF you hb a linear, and are doing it to.... 'save money', I usually find the savings are not there.  I will usually end up with vac input
and output relay's.. and vac relay for bias, vac caps,  and nice metal work.   I end up with a  better overall product that does what I want,
and am happy with it.  IMO, after building everything  from pair's  of 813's  to  4 x 572B's... to  4 x 811A's  to  single and dual 4-1000's, single  3-500Z's
etc, my conclusion after doing this since 1972 is that it's just as easy to build a big amp as a small one. 

##  building a 4 x 572B linear these days is plane nuts.  Add up the cost of [a]  4 x tubes  [b] 4 x sockets [c] 4 x anode connector's,  [d] 4 x suppressors,
etc,  and you may as well use  a  single or dual GS35B...or a single YC-156.    A YC-156  goes for $200-$300.... and No socket required, and NO suppressor required.
Just whack a hole in the chassis..and bolt it it.   Easy to drive [17w = 1.5 kw.... 150w=7.5 kw    200w = 10 kw... it makes for a versatile tube. Linearity is superb,
and it laughs at 100% duty cycle modes. 

##  a  few fellow's here in town  back in the mid 70's  had 30L1 amps.   They would ALL  burn holes right through the  811A anodes.   Several more had new SB-200's.
The fellow's  with the SB-200's  would be buying 572b's  every 2 x years.    In the long term.... you save nothing  using these 'toy tubes' . And none of em were used on   
RTTY/FM or any 100% duty cycle data node..... they just won't last at all.  

##  The bandswitch's and tank circuits in most of these amps are a poor joke as is.  Beware, the current ratings  for multi-tech switch's  are for 60hz..and NOT RF freqs,
esp the higher bands.   If you want a heavy duty bandswitch, either use a bigger switch, and /or  parallel 2 or more wafer's.   If you parallel mutiple wafers, it has to be 
done correctly.  Tank coi taps go to wafer #1..and the output of the assy  is on wafer #2.  That way the RF current will divide equally between the 2 x wafers. 
Switch  contacts  and tank coils, etc... on 29.7 mhz  will only  handle 1/4  what they will handle on 1.8 mhz.  [29.7 /1.8= 16.5     sq rt of 16.5 = 4.1 ]    You can use the same
formulae  between any 2 x ham bands.  

later... Jim   VE7RF