[Amps] Palstar HF2500 amp problem
km1h at jeremy.mv.com
Wed Jan 16 09:05:32 EST 2013
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
----- Original Message -----
From: "Jim Smith" <jimsmith at shaw.ca>
To: <amps at 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
> * 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
> 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
> 73, Jim Smith VE7FO
> Amps mailing list
> Amps at contesting.com
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