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Author Topic: kenwood tl-922a  (Read 2627 times)
W8YK
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Posts: 4




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« on: February 10, 2014, 12:45:12 PM »

i purchased this amp a few months ago and shortly after noticed the load control was at or near zero (fully meshed). i followed the tune-up procedure in the manual and several other suggested methods from the internet. no change. this condition exists on all bands but 10 mtr where peak output occurs at about 4.5 load at 28.0 mhz. someone suggested a soft tube and i wanted a spare set of tubes anyway so i bought and installed a pair  and with the exception of about 10% increase in output nothing changed. i'm working into a dummy load and driving about 15 watts. the only modification that has been performed is the 10 mtr mod. everything else is original. does anyone have any ideas??? thanks in advance
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KH2G
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Posts: 238




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« Reply #1 on: February 10, 2014, 01:01:20 PM »

The TL922 requires about 80W drive and I suspect your not hitting it hard enough to get a proper response.
It's a good and straightforward amp so I'd not expect many problems.
Regards,
Dick
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WB2WIK
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« Reply #2 on: February 10, 2014, 01:29:42 PM »

The TL922 requires about 80W drive and I suspect your not hitting it hard enough to get a proper response.
It's a good and straightforward amp so I'd not expect many problems.
Regards,
Dick

I'd suspect this is the problem also.

The plate impedance when you're driving the amp with only 15W is much higher than the design point and to have a load cap in a pi-net being "fully meshed" when the amp is driven way below its design power level is a pretty common thing.

I notice that with all my amplifiers.  At full power, the LOAD cap works properly: At greatly reduced drive, not so much. Wink

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W1QJ
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« Reply #3 on: February 10, 2014, 03:04:18 PM »

The TL922 requires about 80W drive and I suspect your not hitting it hard enough to get a proper response.
It's a good and straightforward amp so I'd not expect many problems.
Regards,
Dick

I'd suspect this is the problem also.

The plate impedance when you're driving the amp with only 15W is much higher than the design point and to have a load cap in a pi-net being "fully meshed" when the amp is driven way below its design power level is a pretty common thing.

I notice that with all my amplifiers.  At full power, the LOAD cap works properly: At greatly reduced drive, not so much. Wink


Yes, absolutely true, you MUST hit the amp with 80w or better for the load control to come off full mesh (ccw)  Don't be afraid.  Hit it with 30 watts minimum to start to get tune setting then hit it harder and advance the load and you will see the load control start going clockwise as power increases
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KA5N
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« Reply #4 on: February 11, 2014, 03:42:32 AM »

Wouldn't it be better to say: "Increase input power,"  " rather than hit it harder"?
I can imagine a neophyte whacking  his amp with a mallet. 

Allen  KA5N
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W1QJ
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« Reply #5 on: February 11, 2014, 04:33:11 AM »

Wouldn't it be better to say: "Increase input power,"  " rather than hit it harder"?
I can imagine a neophyte whacking  his amp with a mallet. 

Allen  KA5N

Doyle, DO NOT hit your TL-922A with a sledge hammer, mallet, or anything that may inflict physical damage to it.  Rather, increase the input drive level and tune for maximum output power and you will see that the load cap will rise off 1 and go further clockwise.  This is typical of what happens when the amp is under driven.   Roll Eyes
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W8YK
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« Reply #6 on: February 11, 2014, 06:58:17 AM »

well considering the mallet/sledge hammer as a non option thanks for all the help. i tuned up in steps until getting full power out and the load control is working as it is supposed to. i have had amps before but never ran them below 500-700 out as a minimum and so this loading situation never really came up. i was trying to work dx and felt i needed the increased power then. i must be mellowing out in my later years and am trying to run no more power than needed to establish contact. my how perspective and reduced finances change with official retirement. thanks again for all your help and suggestions. i tuned it on high power then reduced the drive to the desired power out and all is well.

doyle w8yk
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K8AXW
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« Reply #7 on: February 11, 2014, 07:19:27 AM »

Doyle, yes, the correct procedure is to tune the amp for full output and if you want to drop the power just back off on the drive level. 
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G3RZP
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« Reply #8 on: February 11, 2014, 07:49:06 AM »

'AXW,

>the correct procedure is to tune the amp for full output and if you want to drop the power just back off on the drive level.<


You know that, I know that and yet there are still people around who are considered 'experts' who say you should adjust loading so that the amplifier has less plate current if you want a lower output. There are times I shake my head in amazement....
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W8YK
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Posts: 4




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« Reply #9 on: February 11, 2014, 11:59:35 AM »

i had read the statement about reducing the power out by adjusting the loading but i missed or did not see any reason for doing it that way. so i'm just tuning it up on hi power and then cut the drive power back on the radio. it seems to work. grid current is good, plate current is good and the plate resonance stays in the same place. everything i have ever read about tuning a final is dip the plate as a last step. i checked it and it was fine. this bears out the philosophy of don't fix it if it ain't broke. 
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N4RSS
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Posts: 258




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« Reply #10 on: February 11, 2014, 12:20:50 PM »

'AXW,

>the correct procedure is to tune the amp for full output and if you want to drop the power just back off on the drive level.<


You know that, I know that and yet there are still people around who are considered 'experts' who say you should adjust loading so that the amplifier has less plate current if you want a lower output. There are times I shake my head in amazement....

I over couple my QRO-2500 on some bands to keep legal limit so that I don't have to adjust drive power.  No big deal.  Brings down screen current a bit. Plus it's directionally the right way if I do have a output spike from the radio for whatever reason.
« Last Edit: February 11, 2014, 12:23:01 PM by N4RSS » Logged
N6AJR
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Posts: 9889




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« Reply #11 on: February 11, 2014, 12:26:14 PM »

A TL 922 is possibly the most beautiful amp made, with possibly the exception of the alpha 87 A, and they work well and the tubes are still affordable. I found the point where you peak the load and dip the plate is the same point when the power out is Maxed Out.  so tune for max output and then back down the input to the amp  a tad to lower the output.
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KI6LZ
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« Reply #12 on: February 11, 2014, 01:02:13 PM »

Maybe I'm not understanding something. If one lowers the drive level to an amp I think one has to retune because the plate impedance has changed. Otherwise the tube efficiency decreases, causing the tube to dissipate (heat up) some more. I never reduce drive to amp, either it's in or out.
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G3RZP
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« Reply #13 on: February 12, 2014, 01:36:33 AM »

You reduce efficiency by reducing drive, but you reduce the input power too, so pro-rata, the dissipation goes down or worst case, stays the same.  The worst case is a very small input - say 1mW. There's no plate current change on the meter so the tube is at its standing dissipation: the efficiency is awful, but the tube isn't over dissipating.

Over coupling has a tendency to improve linearity.

Under coupling in a tetrode stage increases screen dissipation.
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W1QJ
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Posts: 1440




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« Reply #14 on: February 12, 2014, 03:08:14 AM »

Maybe I'm not understanding something. If one lowers the drive level to an amp I think one has to retune because the plate impedance has changed. Otherwise the tube efficiency decreases, causing the tube to dissipate (heat up) some more. I never reduce drive to amp, either it's in or out.


You are correct.  But the concern here is when operating a mode that has an ever changing variety of input power products like SSB, the conventional wisdom is to have the amp loaded for he maximum possible input power.  That would be considered the extreme peaks of the ssb cycle so that the amp stays linear throughout the range and the IMD 3 does not go very high and cause a buck shot effect.  OTOH if one is certain that on a stead state mode like RTTY or CW that the average power and peak power will always be equal, the preferred way to load would be to load the amp for max output a that level and not to drop it back from some higher level.  So it all depends on what mode you will be using as to which way is better.
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