FOR SALE: 300-watt QRP amplifier


CR
 

I have had this high quality, complete amplifier board from eb104.ru around for four years but only recently boxed it up. It uses two robust SD2933s devices, (the cheaper versions of the two VRF2933s used by Elecraft in their LPA500). It is a complete amp on one board that incorporates a sophisticated diplexer (lowpass filters with a high-pass dump load for the third harmonic). I merely added high SWR and current protection plus an antenna changeover circuit. It requires 48--53 volts DC at 10 amps, like from a switching LED supply.

Warning: Driving with a 100-W rig dialed back to 5 watts may destroy such amps. It should only be used with a QRP transceiver.

One more caveat: The 3/8-inch aluminum slab bottom is used as its heat sink. This is adequate for SSB and CW, but not for AM.

$380 shipped CONUS PayPal

Chuck w8mqw


Johnny AC0BQ
 

Ge Chuck
I must tell you, that is some nice looking home brew handi-work.
72
Johnny ACØBQ 

On Sun, Apr 17, 2022 at 4:01 PM CR <maccluer13@...> wrote:
I have had this high quality, complete amplifier board from eb104.ru around for four years but only recently boxed it up. It uses two robust SD2933s devices, (the cheaper versions of the two VRF2933s used by Elecraft in their LPA500). It is a complete amp on one board that incorporates a sophisticated diplexer (lowpass filters with a high-pass dump load for the third harmonic). I merely added high SWR and current protection plus an antenna changeover circuit. It requires 48--53 volts DC at 10 amps, like from a switching LED supply.

Warning: Driving with a 100-W rig dialed back to 5 watts may destroy such amps. It should only be used with a QRP transceiver.

One more caveat: The 3/8-inch aluminum slab bottom is used as its heat sink. This is adequate for SSB and CW, but not for AM.

$380 shipped CONUS PayPal

Chuck w8mqw

--
Check out the 4SQRP website at 4sqrp.com


Dale Putnam
 

How would this match up with a KX3?


From: main@4SQRP.groups.io <main@4SQRP.groups.io> on behalf of Johnny AC0BQ <jomatlock@...>
Sent: Sunday, April 17, 2022 3:27:05 PM
To: main@4sqrp.groups.io <main@4sqrp.groups.io>
Subject: Re: [4SQRP] FOR SALE: 300-watt QRP amplifier
 
Ge Chuck
I must tell you, that is some nice looking home brew handi-work.
72
Johnny ACØBQ 

On Sun, Apr 17, 2022 at 4:01 PM CR <maccluer13@...> wrote:
I have had this high quality, complete amplifier board from eb104.ru around for four years but only recently boxed it up. It uses two robust SD2933s devices, (the cheaper versions of the two VRF2933s used by Elecraft in their LPA500). It is a complete amp on one board that incorporates a sophisticated diplexer (lowpass filters with a high-pass dump load for the third harmonic). I merely added high SWR and current protection plus an antenna changeover circuit. It requires 48--53 volts DC at 10 amps, like from a switching LED supply.

Warning: Driving with a 100-W rig dialed back to 5 watts may destroy such amps. It should only be used with a QRP transceiver.

One more caveat: The 3/8-inch aluminum slab bottom is used as its heat sink. This is adequate for SSB and CW, but not for AM.

$380 shipped CONUS PayPal

Chuck w8mqw

--
Check out the 4SQRP website at 4sqrp.com


Tim N9PUZ
 

On 4/17/2022 4:01 PM, CR wrote:
Warning: Driving with a 100-W rig dialed back to 5 watts may destroy such amps. It should only be used with a QRP transceiver.
Chuck,

I am curious, what is it about a 100W rig dialed back to produce 5W output that causes a problem? Seems like 5W is 5W regardless of the capability of the driving device.

Tim N9PUZ


CR
 

Dale:

Do you recall how the KX3 dials back power? If it does not use ALC, then it should be safe. I never tried this amp with my KX3, which is used as the IF of my 10 GHz rover.

Chuck w8mqw


CR
 

Tim:

Here is a standard warning, in this case from Expert Electronics:

Warning!  There is a small delay in the ALC-system functionality, which may lead to a short-term overload of the external PA. This phenomenon could cause off-frequency emissions or failure of your PA! The User of the transceiver should understand and accept the above, taking responsibility for the potential consequences of using the ALC-system. The manufacturer is not responsible for direct or indirect damages of any kind from using the ALC-system. 

One of my 80m buddies has blown up two ALS1300s with his IC-7300. I personally have seen, with my IC-7300 operating FT8, ALC spikes of 148 volts.


CR
 

Tim:

Make that 148 watts.

Chuck


Dave Benson
 

Hi Tim-

I'm probably duplicating the earlier message, but here goes:

ALC is indeed the mechanism for dialing back power, although I'm not sure how the Elecraft rigs implement that function.  With their emphasis on good CW, it's undoubtedly not a problem.

ALC is a feedback mechanism, and it doesn't act instantaneously- it has a finite bandwidth.  When you go key-down, the rig may take several milliseconds to throttle back to the power you've chosen.  Initially- the full 100 watts- or whatever- is put out until the ALC has a chance to reduce the power output.  Seeing that behavior on a oscilloscope for the first time was a bit of an 'eye-opener'.


73- Dave, K1SWL


On Sun, Apr 17, 2022 at 6:33 PM Tim N9PUZ <tim.n9puz@...> wrote:
On 4/17/2022 4:01 PM, CR wrote:
> Warning: Driving with a 100-W rig dialed back to 5 watts may destroy
> such amps. It should only be used with a QRP transceiver.

Chuck,

I am curious, what is it about a 100W rig dialed back to produce 5W
output that causes a problem? Seems like 5W is 5W regardless of the
capability of the driving device.

Tim N9PUZ







William Franklin
 

The Icom 718 is one rig that has that ALC overshoot.  It was noted in the QST review and my rig showed a 150% overshoot.  Possible damage to solid state amplifiers was suggested.  So, beware, check it out properly.  Even if your rig checks out ok, I'd be willing to bet at some time or another an operator error will occur if that higher power input is possible.  Been doing this stuff for a long time, seen a lot of errors, and even committed a few myself.  But, as a wise man once said "Experience is what you gain when the results don't turn out as you expected."  For me, it is probably not worth the effort to turn back a 100 watt rig to drive a 300 watt amp.  But, then, that's just me.  Just be careful!

73, Bill, K5WB


From: main@4SQRP.groups.io <main@4SQRP.groups.io> on behalf of Dave Benson <davek1swl@...>
Sent: Monday, April 18, 2022 7:45 AM
To: main@4sqrp.groups.io <main@4sqrp.groups.io>
Subject: Re: [4SQRP] FOR SALE: 300-watt QRP amplifier
 
Hi Tim-

I'm probably duplicating the earlier message, but here goes:

ALC is indeed the mechanism for dialing back power, although I'm not sure how the Elecraft rigs implement that function.  With their emphasis on good CW, it's undoubtedly not a problem.

ALC is a feedback mechanism, and it doesn't act instantaneously- it has a finite bandwidth.  When you go key-down, the rig may take several milliseconds to throttle back to the power you've chosen.  Initially- the full 100 watts- or whatever- is put out until the ALC has a chance to reduce the power output.  Seeing that behavior on a oscilloscope for the first time was a bit of an 'eye-opener'.


73- Dave, K1SWL


On Sun, Apr 17, 2022 at 6:33 PM Tim N9PUZ <tim.n9puz@...> wrote:
On 4/17/2022 4:01 PM, CR wrote:
> Warning: Driving with a 100-W rig dialed back to 5 watts may destroy
> such amps. It should only be used with a QRP transceiver.

Chuck,

I am curious, what is it about a 100W rig dialed back to produce 5W
output that causes a problem? Seems like 5W is 5W regardless of the
capability of the driving device.

Tim N9PUZ







Chuck ke9uw
 

The K3 (s) does a slowish ramp up to the desired wattage. At first I thought it was a fault, but I believe it's designed to beat the ALC overshoot issue. I haven't tested the KX3 in this regard, however I would guess it's the same.