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AL-811 amp question.

C

chris.s

Active Member
Dec 4, 2005
107
5
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Hello to everyone on the forum,I just picked up a al-811 amp with new Taylor tubes,the problem I'm having is tuning the amp up on 10 meters,it has the 10 meter mod done,It tunes up fine on all the bands but 10 meters,the input has been tuned for a low swr between the radio and amp,that took a very small tweek and it was done,I have tried tuning it in several different antennas,two different legal limit dummy loads all with the same result,on all the other bands it runs around 145-150 ma.grid current when running full power(80-12meters),but when you try to tune 10 meters the grid current shoots past 200ma.In order to keep the grid current down I can only put around 20 watts of drive into it for an output of 200-250 watts out,someone said the bandswitch could be the problem but would that not cause an issue with 12 meters seeing they both use the aux. position,also I put the original tubes back in it with the same results good everywere but 10 meters,I know the owner and amp since it was new and I know it spent it's life on 40 and 20 meters and very little use on any other bands if that makes a difference,any ideas on the problem is welcomed,I dont try to many different thing with it because of the high grid current,also tried jumper length changes with no change to 10 meters.


thanks for any help.

Chris.s
 

Chris,
I think what you are seeing is about normal for an AL-811 on 10 meters. Something on the order of 50 - 60% output power can be expected. There are lots of qualifications with that and it depends on each amplifier and operating situation.
- 'Doc
 
Chris Ive just seen this happen with a AL-80B a guy just purchased brandnew here in Central Wi. He is seeing 500 - 650 watts on 10 meters when the amplifier will do 1 KW or more on 80 meters the amplifier has 1 3-500Z tube.
 
811 problem

thanks for the replies guys,I think I'll leave it alone,I have an 811h and a Tokyo high power that work fine on 10 meters so I'll call it good,one more quick question can the AL-811 be converted to 6 meters if it had 572b tubes,I've seen several Heathkit amps that run572bs that have had the conversion done to 6 meters.


73s and thanks again.

Chris.
 
Maybe one of the other guys can chime in on this I personally do not know anyone who has done this but I will say the 572B is an outstanding and rugged tube I love mine ;)
 
A 572B amp is not a good choice for converting to 6m. The 572B tube is rated to only 30 MHz for full ratings and the lead length is too long for good 50 MHz operation due to the high capacitance it creates. Combine this fact with the fact that you have three tubes to deal with and the total tube capacitance will be very high making it almost impossible to find a plate tune capacitor with a low enough minimum capacitance to tune the amp. In fact the total tube capacitance may actually exceed that required to resonate the amp even before adding the tuning capacitor. A 3-500Z type amp is much better for conversion to 6m as they are good to at least 100 MHz. The best Heath amps to convert to 6m is the SB-220 which uses a pair of 3-500Z's. The SB-200 which uses a pair of 572B's can be done but it wouldn't be my first choice to convert.
 
811 on 6 meters?

In a short answer "NO"! A HUGE waste of MONEY & EFFORT even with 572B tubes.An amp with 3-500's or 4CX250's would be PERFECT for a 6 meter conversion.The 811A is NOT designed for 50 MHZ usage.

SIX-SHOOTER
 
I know some of the older tube amplifiers were converted for 6 meters but I havent seen any newer type amplifiers done up that way and this as explained above about the tubes is most likely the reason why ;)
 

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