AL811 160M Problems

[flintstone mop]

Hello All,
I have discovered a weird problem with my AL 811 amplifier. I wanted to try it out with the reasonable band condx of 160M, and get some sig reports. Hopefully 599
When I keyed up the amp, from my AF67, the freq meter read twice the freq of 1880. The Bird wattmeter read high SWR.
I'm feeding the amp with 12 watts from the Elmac, but I keep getting a freq doubling effect on the output of the AL 811 (3 ea 811A's for 600W P.E.P.) Under nice band condx that should get through pretty nice.
Any body have any suggestions of what is doubling the freq??? to 3770???  Would there be a lot of 2nd harmonic in the AF67 that the amp picks that out as the freq to amplify?? (should I try to align the input circuit to the AL811??) Looking at the RF ouput on a 'scope the freq starts to double as I tune the amp and get around 100 watts. I cannot even get 600W on 160M. The other bands are perfect driving the amp with the Elmac.
I will try to drive the AL811 with my Kenwood TS440 to find out who is giving me grief.
thank you

Fred

[WA1GFZ]

Try the same thing into a dummy load.

[Steve - WB3HUZ]

Check the output of the Elmac to make sure it is not tuned up on a harmonic.

[flintstone mop]

OK FINE.....And Steve the QSO was good stuff.....W3TIM was holding court throughout.
I'll have to devise some way to look at the Elmac on a spectrum analyzer or mabey the Flex software can help me here??? Or would the bandswitch of the R390A be the limit point???
I would have to lug an expensive piece of equipment home from work. And I don't want to bring Ham projects to work.

Frank, I thought I was ok in the dummy. A light went on in my head AFTER I switched to the antenna and saw the skyrocketing SWR and THEN I looked at the freq counter reading 3770.
fred.......more to come

[K3ZS]

Just checked with my AF-67.    On 160M there are two dips on the plate tuning.  Going clockwise, the second dip is the one for 160M.

[flintstone mop]

OOOPs
Bob,
I forgot about that little quirk.....I'll check and see what dip I'm on. Might be the key. All the fun stuff has to wait till later tonight.

Fred

[Steve - WB3HUZ]

Something is tuned on a harmonic. 2 x 1885 is 3770.

[w3jn]

Fred, all these problems you're having on 160 - have you checked your antenna???

Do these amps load up correctly into a dummy load?

[flintstone mop]

Hi John,
Any small AM rig driving a linear is tuned and smoked in a known good dummy load first.
The first sign of weirdness was after the dummy load TO THE antenna and the high SWR on the Bird that is always in-line for any RF going out of the shack. I looked over at the freq counter and saw 3770........and red lights flashed in my head!!!!!
More later....berfore the ice covers Western Pa.

Fred

[WA1GFZ]

could this be the reason the other amp is smoked???

[flintstone mop]

The Titan amp had a spat of arcing in this area of the bandswitch, a year ago, and the problem disappeared. Went through the same checks for intermittent coax,relays, ants, dummy, etc,etc.

Dummy load and antennas are good and near 1.5:1 generally. Nothing shows up as intermittent.

I spent some time with the AL811 amp and the Tune control makes for freq doubling NOT the AF67 as I first suspected. The AF-67 station was invented for better band condx on the upper bands. 40 and up.

I thought I might experiment and press it into service for 160M. But with only 600 P.E.P. it would'nt be any better than a DX100. I wouldn't want to put a QSO through low power on 160M when the band is busy. A little head scratching took place last night.

The Titan amp will ship and hope that it doesn't get too $$$$. I do not have $2700 for an AL82 which is a respectable amp with a healthy P.S. and two 3-500Z's.

All of this rig-am-aroll, with these linears, is for easy QSY and legal limit power for A.M. and then the SSB contest on 160M end of FEB 2009. The AL811 would sqeek through the SSB contest. There shouldn't be any difference in receiving 600W P.E.P. and 1500 P.E.P. Barely an S-Unit.

Fred

[flintstone mop]

I was on the air SUN  night DEC 21 with W1VD, K2PG, KN8AZN(?) with the AF67/AL811 amp combo and everything is ok. 125 watt carrier and no sign of second harmonic from the AL811. It was definitely mistuning of the TUNE control on the AL811 that gave me the problem that started this thread.
Conditions were very nice and got by with gud 599 reports with 125 Watts.
Thanks for the tips and the mental excersize.

Fred