|SB-200 QSK mod using W7RY boards off ebay - relay timing
||[Mar. 27th, 2013|12:56 am]
I've finally completed the SB-200 QSK modification using the board designed by James Colville, W7RY, available on ebay. Here is some additional info about the modification as well as some interesting relay timing traces.
This board requires the following changes to the original SB-200:
- removal of the entire ALC circuit
- removal of the SWR metering bridge and circuits
- complete rewiring of the metering switch. The Rel Power and SWR positions now turn on the STANDBY mode. The Rel Power pot is disconnected.
- direct grounding of the 572b grids
- un-grounding of the R12 on the power supply board and wiring it to the (new) grid/plate metering circuit
After completing the mod I'm getting 750-800 watts on all bands, and a whopping 900 watts on 10m, with about 60W drive. This is with a new pair Chinese 572b and 125V mains voltage (see previous post on adjusting the Vf). The semi break-in operation is very smooth, almost as quiet as the Tx switching on the TS-590 radio.
There are three relays controlled by this QSK board: RF input reed relay, RF output vacuum relay (e.g. Jennings RJ1A), and a solid state (optocoupler) cathode bias relay K3. Pushing PTT will make the QSK board energize all three of them at the same time. The order of switching is influenced only by the transfer speed of each individual relay.
The actual contact closure will occur in the following order:
W8JI or NE7X recommend a different sequence for a fail-safe operation. It needs to be 3,1,2, i.e. the cathodes should be grounded last, which will turn ON the amplifier.
- input reed relay (spec 0.6 ms, measured ~0.4 ms) - Trace 2
- SS relay (spec 1ms, measured: ~0.5 ms) - Trace 1, and Trace 4
- vacuum relay (spec: 6-8 ms RJ1A, measured >1ms) - Trace 3
Because of this, slightly different, order the W7RY's board requires to be careful that the exciter is OFF until all three relays are done switching. If there is any RF present on the input before or at the same time with the PTT signal, it will make the output relay "hot switch". The one I got (jennings RJ1A) is not rated for hot switching, costs $60, and not easy to swap!
Most of the modern rigs will have a at least 10ms lead time for PTT, which should be safe for this board. But I'd rather have the correct timing on the T/R relays in the amp.
Trace 1. RF Vacuum relay and Cathode bias. Bias is removed ahead of the RF out relay:
Trace 2: PTT and RF Input relay 432us:
Trace 3. PTT and RF Out relay 1024us:
Trace 4. PTT and Cathode bias solid state relay 536us:
Note: I've attempted to correct the timing problem by doing a mod to the mod (hi). I'm currently testing and may post some info later.