EB104 amp project

[NQ6U]

I'll take two!

[mw0uzo]

Thx guys :)
Had a good few QSOs tonight on it on several different bands. Had a distortion problem on 80m at high powers, I think due to forgetting that the fast current protection is set really low for testing (bias reduces at ~300W).
Off to bed now, I might be able to do some more work on it after Christmas so I'll post some updated photos of the innards then.
Have a good Christmas and I hope you consume shocking amounts of alcohol :D
Dan

[mw0uzo]

Current state of project


Changes since last photo of insides:
Built and installed LPF modules
Got rid of big RXTX relay, input SWR just started to rise at 28Mhz.

Things left to do preventing proper use:
* Attenuator module needs building and wiring in
* RF pickup problem in LPF modules, fitted bypass capacitors to control board but this had no effect. Next solution to attempt is to rewire the control lines using screened cable.
* 40m LPF SWR is too high, also a few interconnecting wires need to be changed to thin coax to reduce SWR at 30Mhz.
* Replace 3.5mm plugs to SWR modules
* Fit relay to bridge out main transformer inrush limiters. When the amp is cold and suddenly transmits a large amount of power, the protection trips with a low Vs fault.

Other features left to do:
* ALC
* Auto frequency detect

Firmware is working well, not had a single crash during recent testing :)
* Need to write peak detection for the power meters
* Fix some monitor screens so they actually work properly
* Make amp store its current state in EEPROM.

[mw0uzo]

I think I've solved the RF pickup problem. Changing a 10k resistor to a 510 ohm in each transistor switch for each relay appears to fix the problem. I have also added some heavier duty ground straps between the lpfs and control board which has reduced rf measurable between the control board and lpf grounds.

[mw0uzo]

Fixed RF pickup problems - confirmed. Modified relay boards to improve SWR at 30Mhz. Changed 3.5mm plugs for SWR modules.
Found some solder spheres on the 40m LPF. Removed them, but SWR is still highish (1.7) at the amplifier. However, now the SWR does not increase with power and the amp performs well at high power. I think I will leave it as it is and raise the pre-lpf SWR warn and fault levels.
Fitted cable to enable programming with amplifier case closed. Replaced all the thick RG-58 cables which were quite inconvenient to thin teflon coax - looks a lot better and amp is easier to inspect and work on.
Installed soft start relay.



Going to try some more test QSOs tonight to make sure its working properly.

[mw0uzo]

I've got a gap in the middle. Wonder what to fill it with. A homebrew autotuner? That might be difficult to fit in that space.. plus a load more work. Maybe fill it with a plate for holding spare fuses? Any suggestions?

[NQ6U]

Espresso machine? You can use the waste heat from the transistors to boil the water.

[mw0uzo]

A very sensible suggestion, thx. Perhaps one of these as well?

http://www.lolr.de/2011/06/14/this-m...ys-everything/

[mw0uzo]

Check this out: http://www.youtube.com/watch?v=sUtS52lqL5w
Sod the amp, its a pain in the arse, I wanna make one of these!

[NQ6U]

Magnificent! 600 hours spent to build a machine to move a bunch of balls back to their starting point in as complicated a manner as possible. This is not unlike a lot
of the jobs I've held over the years.