Opcom
Patrick J. / KD5OEI
Contributing
Member
Offline
Posts: 8265
|
|
« Reply #4 on: May 02, 2020, 07:50:53 PM » |
|
If I saw one of these for $80 and it had good iron etc I would buy it immediately.
I posted late not seeing the last post but for what it;s worth;
The one on BunkerofDOOM is mine and graces a rack in that hallowed hall. For over 10 years there have been no troubles. The 4x250Bs are cheaply had, but nothing has ever happend during use to ruin them. You can run 866's, 3B28s, or solid state sticks with no changes.
The terminal strip on the back has 1KVDC, 400VDC, 110VAC, and -150V on it, so be careful. Most of it is for an external mod scope, SDP No. 1S. Opening and closing a contact on terminals 5-7 controls cutoff bias/normal bias. This is a non isolated 110VAC circuit.
There is no built-in T/R relay, but there is a manual amplifier in/out switch. So you will need a Dow Key or whatever to automate it.
I know more than one guy who flips 3 or 4 switches going from RX to TX.
BTW this is designed for 110V, so a good idea to buck the line a bit or at least adjust it so the heater voltage on the tubes is correct. It should have a 15A outlet or equivalent.
On AM, I got 100W carrier, 400W PEP easily from mine. Trying for 500-600W on AM is likely to trip the plate current overload. However, when operated within its ratings, it is a wonderful general coverage amp.
The power supply is rated 1KW DC, CCS duty; 2KV@500mA. The amp is also rated for continuous duty on SSB at that average level, which ought equate to 2000W PEP input (no compression obviously).
I found the blower a little weak IN MY OPINION but then I like overkill air. Nothing actually overheats and it's pretty quiet. If one wishes, a larger blower can be attached via a hose and a home made adapter to the simple screened intake hole on the back. Just make sure the blower is actually running because it is quiet.
No input tuning is required.
Drives very easily, says 100W PEP, but I found it to work OK with less.
Grounded Grid circuit, AB1, using the normal AB1 element voltages on the tubes (as Eimac says to do)
I have indeed seen the screen current go negative when properly loaded at full power. The screen current meter is a fine aid to loading it and helps avoid overloading the screens.
Here are the Ratings from the Plate Power Ratings chart in the book, since you have the unit and should be careful with it til you know it. Because it's a little unusual, The manual's procedure is really needed for tuning it properly.
CW key down conditions (continuous): drive 30-40W input 1000W output 575W
====================
SSB: average meter reading on voice peaks drive 40-50W input 1000W output 625W
PEP 2-tone test drive 65-80W input 1600W output 1000W
PEP voice drive 80-100W input 2000W output 1250W
====================
AM carrier with DSB drive 15-25W input 700W output 300W
|