Need Amp Recommendation

[NightThumper]

Brian read the edit to my post after you had already quoted it. Yes you would definitely save some money…then again if you mess it up…POOF no more amplifier. Again I’m back to the KISS principle…keep in mind David has what I would call a high level of technical competency…for him this type of modification is a walk in the park.

 

[Dmans]

I believe the trimmer in the picture above is the same as this one circled in red. I measured it at 20-130pF.

73
David

 

[Brian G]

^^^^^^^^^^^^^^^^
Above post edited to include a picture from the Palomar Skipper I did for a friend a few years ago. You can almost make out the part number on the trimmer capacitor. Looks like "303" I wouldn't swear this is an Arco trimmer but they are available.

Something like this? https://www.ebay.com/itm/143261935930

 

[Brian G]

Brian read the edit to my post after you had already quoted it. Yes you would definitely save some money…then again if you mess it up…POOF no more amplifier. Again I’m back to the KISS principle…keep in mind David has what I would call a high level of technical competency…for him this type of modification is a walk in the park.

Yep definitely thought about that.

 

[Dmans]

Something like this?

Yes. That is the bulk of the modification.

If it were my amplifier, I would be seriously tempted to remove the single driver tube and drive the 2-8950's directly. But it is not my amplifier so you have to decide for yourself.
Selling the amplifier now is an option.

Selling is a crapshoot if going through Flea-bay. Protection for the Seller in this situation is pretty much non-existent.

Finding just the right local operator to you to offer something reasonable for your box of tubes could prove difficult. That operator will inevitably be facing the same scenario you have now and may not be satisfied. Could create some bad blood and cost you a friend.

73
David

 

[Dmans]

One other note. As mentioned previously in this thread, I currently have an AL811H on my bench that looks great on the outside but the inside is a disaster. It was used exclusively on 11 meter SSB and it appears every tube in it flashed over and created a lot of problems.
It is slowly on the "rehab" road but still has a way to go.

73
David

 

[groundwire]

its clear you don't want to spend the money on real equipment so just buy a texas star and be done with it....

 

[Brian G]

Brian read the edit to my post after you had already quoted it. Yes you would definitely save some money…then again if you mess it up…POOF no more amplifier. Again I’m back to the KISS principle…keep in mind David has what I would call a high level of technical competency…for him this type of modification is a walk in the park.

I've decided to go with the tuner. I figure it is the lowest risk, will hopefully give me a couple more years out of the amp, and saves me at least $800 in the meantime. Perhaps I will try the DMANS fix at some point as well....
Thanks.

 

[Brian G]

its clear you don't want to spend the money on real equipment so just buy a texas star and be done with it....

Has nothing to do with not wanting to buy "real" equipment. I said earlier I would spend the money if I thought I was getting a good solution. But there really is no reason to scrap the one I have now since it is working well and has suited me for many years. Someday it will go and then I will buy something better--though I am still not sure what "better" is based on all the comments here. BTW, I was not sold on the Texas Star to begin with. I was leaning towards the 811 but another poster advised against it based on it's design.

 

[w9cll]

W9, I would not recommend the 811\811H to be used on 27 Mhz.
They are not designed to run on 11 meters.

Thanks for the info, admittedly I am not an amp guy, I have never found a need for one.

 

[BJ radionut]

Ameritron AL-80B Ameritron HF Power Amplifiers | DX Engineering

Ameritron Amplifier | Page 2 | MFJ Enterprises Inc

Ameritron Amplifier | Page 3 | MFJ Enterprises Inc

 

[BJ radionut]

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[Brian G]

Brian G,
If you add the input tune control to the amplifier as it is, it will allow you tune the input section of the amplifier to a better match to your Stryker. Not unreasonable to expect less than 1.5:1.

If you eliminate the first driven tube and drive the next section (2-8950's) and add a tuning coil* to that section, it will allow a larger drive (since now you would be driving 2-8950's instead of 1-8950) and allow a tunable input to that 2 tube section. It may or may not take the full output power from your Stryker but should make the amplifier less prone to gain issues.

(*The amplifier may include a tunable Pi network for the 2 tube section. I will look at the schematic and see)


A simple tuned input circuit below. The black coax goes too the driver tube (8950 in this case) cathode, the tan coax comes from the relay. There is a $5.00 trimmer capacitor and about 6 inches of 14ga solid wire and 2 wire terminals added.

View attachment 45525


73
David

hi could you give me a bit more specifics on how to bypass the first tube as mentioned above? Parts, steps. Thanks!!

 

[nomadradio]

For that model? No.

But here's how we did this for a one-driving-two amplifier. If your first pre driver tube has a plate cap, the layout will be a bit different.

https://www.worldwidedx.com/threads/kris-power-pump-becomes-a-straight-2-tuber.262052/#post-766473

73

 

[Dmans]

Brian G,
While I never seen a PAL 750B much less owned one, here is what I believe needs to happen to bypass your single 8950 driver.
(This snippet clipped from the full schematic included below.)

A couple of points to ponder:

The 5-50pF variable capacitor would, in this configuration, serve as your input tune control. It may need to be made a larger or smaller value as well as the "9 TURNS" coil it is in series with. Again a "cut and try" method.

RY2 shows a relay contact controlled by the "150/750" switch on the front panel. If the switch is grounded (to activate the relay coil) so will your input RF be grounded. I would wire around the relay contacts to prevent this or disconnect the wiring from the rear of the 150/750 switch to prevent grounding the negative of the relay coil.

As far as rewiring the input from the cathode of V1, you should use a section of 50 ohm coax cable with the shield attached to a good chassis ground at both ends of the cable.

The 400VDC wire going to the Plate Cap of V1 will have to be removed and well insulated from any other components or chassis ground.

THERE ARE VERY DANGEROUS VOLTAGES INSIDE THIS UNIT.
THEY CAN KILL YOU!!!!!!!!!!!!!!

The schematic is included here as an attachment so that others may chime in on this "theory" of bypassing the single stage driver of this unit. Again, I have never owned, operated or seen one of these amplifiers.

73
David