[Top] [All Lists]

[AMPS] Heathkit Warrior (HA-10) questions

To: <>
Subject: [AMPS] Heathkit Warrior (HA-10) questions
From:" < (Mitchell Carson)
Date: Mon, 03 Sep 2001 12:55:37 -0500
Hello all,

I recently picked up a somewhat working Heathkit Warrior, complete with 4 
572B's.  Primarily, I picked this thing up to learn about tube-type 
equipment.  My plans are to eventually build in T-R switching and proper 
grid bias circuits.  Before I do that though, I have encountered a problem 
with the amp and I'd like to run the problem past you experts.

The issue I'm facing is low plate current.  According to the assembly docs, 
the amp should exhibit resting plate current of 90 to 100 ma (after full 
warm-up of the 866A's).  Plate voltage is good at 1650 volts.  Grid current 
is zero at idle.  Resting plate current is only 50 ma.

I've connected my transmitter, dummy load, and watt meter to the amp. 
 After warming up and tuning it with 5 watts drive, I brought up the drive 
on the transmitter.  With 100 watts of drive, I can only get 250 ma of 
plate current out of this amp.  Grid current is 125 ma.  Plate voltage 
doesn't drop during transmit.  As a result of the low plate current, the 
amp will only produce 500 watts with 100 watts of drive.

I originally suspected the 572B's.  A friendly local elmer loaned me a set 
of brand new RCA 811A's.  I installed them and tried again.  Resting plate 
current dropped to 45 ma with the 811A's installed (as compared to 50 ma 
with the 572B's).

Looking through the troubleshooting section of the assembly docs, low 
resting plate current could be due to:

1) Cut-off bias not shorted.  I've made sure that it is. No change.

2) Improperly neutralized.  I've tried adjusting the neutralization 
adjustment while HV is applied.  No changes.

3) Open or damaged parasitic chokes.  I've checked for continuity across 
the chokes and they conduct.  I may build some new ones though (7 1/2 turns 
of solid 16 ga on 51 ohm 2 watt "non-inductive" resistors).

4) Check bias capacitors on the tube sockets to make sure they're grounded. 
 Although I haven't replaced those .02 uf disc caps, they are connected to 
ground and the connections are good.

5) No bias on pin 3 of the tubes.  I've checked for voltage there.  The 
assy docs details a measurement of -4.5 volts.  I measured -4.71 volts.

Folks, I'm stumped.  The only other component that might be troublesome is 
the 1000 uuf 5 kv tubular cap that mounts between the neutralization 
bracket (at the tuning capacitor) and the copper strap going to the plates.

I'm obviously new to tube-type equipment, and I'm trying to learn as I go. 
 Any words of wisdom from others who have "been there...done that" are 
greatly appreciated.

VY 73,
-Mitchell / W5MEC

FAQ on WWW:     
Administrative requests:

<Prev in Thread] Current Thread [Next in Thread>