Those amps have a history of cooking the plate blocking capacitors. They
heat up, detune the amp which reflects back to the input since there is low
reverse isolation in a GG amp.
Id start there before worrying about soft tubes. Those can be checked one at
a time with 30W drive on 20M. Stuff a paper towel in the empty hole
Carl
KM1H
----- Original Message -----
From: "Jim Smith" <jimsmith@shaw.ca>
To: <amps@contesting.com>
Sent: Tuesday, January 15, 2013 8:10 PM
Subject: [Amps] Palstar HF2500 amp problem
I'm trying to get a Palstar HF 2500 amp working that I bought off e-
bay. I need help with this.
Problem is lack of output power.
I ran some tests as follows:
* Drove the amp with an IC 706MkIIG (My MkV is broken).
* Measured amp input SWR with ancient Heath SWR bridge.
Still works, though. Shows SWR of less than 1.1 to 1 on my dummy
load.
* Measured amp Po and load SWR with new Daiwa 3 kW power meter.
* Used my antennas as loads (Dummy load can't handle 1500W)
On 10-20m antenna is R5 vertical
On 40m antenna is a too short 40m dipole.
No functioning 80 or 160m antenna.
For each band with an antenna
Set VFO to 1 kHz above bottom of band, tuned for max Po as follows:
Reduced 706 output to min
Went into xmit mode
Increased 706 output to get some output power
Adjusted Tune & Load for max Po
Increased 706 output while adjusting tuning for max Po
In many cases couldn't get more than 40W or so out of the 706.
Measured Ig, Ip, Pin (according to 706 meter), SWRin, Pout and
Preflected
Ditto for VFO at mid-band.
Ditto for VFO at 1 kHz below top of band
The only frequency I got rated Po (1500W) was 7299. SWR 1.5:1
Suggests tubes are OK
Got 1050-1100 W at a couple of others
Lots of 700-900W readings
Quite a few 300-500W readings, some into 1.0:1 SWR
No correlation that I can see between max Po available and load SWR.
However, on every band the input SWR is about 2:1. It was worse on
some bands before I adjusted the input tuning on each band (mid-band -
as much Po as I could get) for lowest SWR.
Since then I put it on a friend's 1500W Termaline dummy load and drove
it with his FT 1000D (with ant tuner).
Only tried it on a couple of bands but couldn't get more than about
1000W out.
That was with a Pin of 50-60W max.
Po sagged about 30% over about a 1 minute period of key down. Input
SWR went up and Pin went down over this same period.
Didn't record or remember how much.
Didn't retune 1000D tuner to see what happened - should have
Ig was typically 30-40 mA.
Factory tune chart shows:
Ig of 8-30 mA for, depending on band, Po of 1125 to 1950 W.
Pin of 20-60 W
SWRin ranges from 1.0 to 1.5. Average is probably about 1.25
Some anomalies we noticed.
Red Transmit LED comes on sometimes but not others and brilliance
varies under key-down cndx.
This scares me because it is driven directly by an output of the
PIC. If the PIC goes, nothing else matters.
Idle Plate current
Manual says that it should be approx 120 mA
Actual wanders between 20 mA and approx 200 mA.
Need to recheck the 200 mA. Definitely at least 120 mA
Haven't noticed any correlation with anything else.
Tune capacitor settings
Actuals very different from factory settings on many frequencies
and quite close on some others.
At 29.699 actual Tune setting was 0. Factory didn't test that
high but they got 18 at 28.500
Load capacitor settings
Actuals were somewhat different from factory settings.
At 29.699 actual Load setting was also 0. Factory didn't test
that high but they got 7 at 28.500
I'm hoping that someone will be able to suggest reasons for the
behaviour I'm seeing and/or things I might try to get this functioning
properly.
73, Jim Smith VE7FO
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