[Amps] HV lytic max V ratings..some notes

[Jim Thomson]

Date: Wed, 14 Apr 2010 09:27:50 -0400
From: "Carl" <km1h at jeremy.mv.com>
Subject: Re: [Amps] HV lytic max V ratings..some notes


> ##  alpha used 1N4007's in their 374-A no tune.. pure junk. [diodes]


** Dont know of any failure issues. Later models went with the 1N5408 as the 
price difference came down to almost nil.

## 1N5408's were 40 cents each, in 1976.   1N4007's  are failure prone.
Peak rep is way too low, surge is too low.  How cheap could they get ? 





>
>
> ###    I can hear the diff with ESSB.   I can also hear the diff on AM. 
> I'm not
> talking abt 120 hz ripple either.  The ESSB  audio sounds cleaner.. as 
> does
> AM audio.   I haven't tried FM..yet.


** Then you are in a very small group.

##  agreed.  After the yaesu MK-V RX mods, [including bypassing the entire yaesu
AF junk], easy to now hear any defect.  I shut off their RX DSP junk as well, since it's 
not done right, and adds yet more distortion and...'digital grunge'.  The stock yaesu
1.5 w @ 15% THD AF amp is a joke.  Ditto with headphone amp. I tap off the Analog
RX product detector.. then  straight out externally.. to outboard Class A audio amps.
As a  side note, the stock yaesu  MK-V,  TX DSP is more crap... the noise floor increases by
21 db, when toggling between Analog SSB.. and DSP SSB. [mic gain on zero] 




>
> ### say what?    The alpha's all have a 3.5 kva CCS xfmr... and so does 
> the  AL-182/1200/1500.    So does the ten tec centurion.


** Say what?? You better get your glasses on and read an old Dahl catalog.

##  any 1.5 kw  CCS out amp with 50-60% eff... will require a bare min
of 3000-3500 va ccs xfmr.  You can  buy the alpha 3.5 kva CCS xfmr,
as used in all their recent amps, including the 91/99/87A..from their site. 


>
> ##  so what's wrong with big C filters then?  You can buy surplus  big 
> 2300uf +  caps for the same price as new   330uf  to 560 uf vcaps.   An extra  FREE
> 100-200 w pep out and better imd, is nothing to sneeze at.


** Eimac didnt use ridiculous amounts of C to establish tube specs which are 
usually well above the crap SS rigs in use. I can understand 330-560uF which 
still may place a strenuous starting load on stock amps.

## install step start....pretty simple. 


## any two tone test doesn't require much of anything.  Everything is in a 
steady state, including fil v, bias V, B+, etc.  Eimac used 3 phase B+  supplies,
well filtered for their various imd tests. 

## Now toss in B+  supplies, where the B+ is all over the map.. and worse yet,
those silly RF chokes heath used on the SB-220's grid  [or Measures 30 ohm grid
resistor's] on modes like SSB... and IMD  will degrade.  The SB-220 grid chokes
have a 25 ohm DC resistance.   150ma grid current per tube x 25 ohms =3.75vdc.
150 ma x 30 ohm grid resistors = 4.5 vdc.   Stock zener is 5 vdc.   So BIAS  will 
vary  from 5 vdc  up to 9.5 vdc .  That's real lousy bias regulation.... yo-yo, when 
driven on ssb. 

## those  200 pf caps  from each grid pin to chassis are a joke. IMD is worse, when
they are installed.   Grnd  all 3 x grid pins with wide Cu strap, and  Drive requirements
DROP 20-25 watts. [ before and after.. with calibrated wattmeter's on both sides of the
amp]   The amp is more stable with the grids directly bonded to chassis. Power out on 10M
goes up a whole bunch. 


>
> ##  P-P voltage drops  from 210 V.... down to just 16.8 V  P-P


** I never saw a Drake with only 210V PP drop. The iron is only .8A CCS. 
Thats .4A after it is doubled which is half  PEP Ip.
What does it do key up-key down?

##  Lemme  re-phrase that.  With a 800 ma DEAD CXR... the PEAK to PEAK
RIPPLE, is 210 V.  That's  with stock 25 uf filter cap. [200uf /8]

##  With  312.5 uf  [2500/8].. and the same 800 ma dead cxr, the PEAK to
PEAK RIPPLE  is now 16.8 v   Dyanamic regulation is superb. 

##  B+  is  2650 vdc  on RX...  and drops to 2605 vdc, when  sucking 145 ma
ZSAC.     B+ drops to  2485 vdc.. with a 800 ma CXR.   This is with stock 25 uf
filter cap.  That's using both the built in B+ meter, on all 4 x drakes.. and also
a Fluke 0-6kv dc HV probe and a fluke 87 DVM.  Now with a 50 ohm-50W  WW 
glitch installed,  with a 800 ma cxr... B+  drops another 40 vdc [.8 x 50 ohms]
.... and B+ is now down to   2445 vdc.   This case is with 25 uf stock filter. 
With 312 uf, all numbers are up by 28 vdc. [800 ma cxr]  On SSB, B+ meter
barely flicker's. 




** I still have the 51.5UF @ 10kv Sangamo on a bottom shelf for some future 
project. I believe it is over 150# but its been 20 years since I moved it. I 
couldnt store wimpy lytics that long. 

## kinda tough to stuff a 150 lb cap into a MLA-2500.  51 uf isn't big 
enough anyway.  Heck, even Emtron figured it out.. and used 112 uf.  
A 2500 uf cap weighs 14 oz.  10 A ripple current rating. 



** Meanwhile most of us are grounded in the real world and happy with using 
270(current Ameritron stock)-560uF during replacement time since they at 
least fit existing amps.

##  stuff the biggest caps that will fit into these desk top amps! 
270/8= 33.75 uf  = 151 joules [3 kv]    1 joule = '1 x watt second'
1.5 kw out at 60% eff  requires 1500/.6 = 2500 watts DC input. If you only have
151 joules of energy stored up, no wonder the B+  sags on ssb!  A stock SB-220
is even worse with it's 25 uf =  112 joules.
315 uf @ 3 kv = 1406 joules.... no sag on ssb... and way more pep out.
Instead of knocking the concept, maybe you should try it. Better dynamic regulation
was the primary goal.  The reduced ripple was a secondary benefit. End result is  more
pep out, less IMD. 

later... Jim  VE7RF  





Carl
KM1H


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> Jim   VE7RF
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> Carl
> KM1H
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