[AdrianH]

I have tried using my radio test set to measure the amps output as it allows settings for measuring dBm's into 4 Ohms.

At 1KHz the amp manages to get to 38.6dBm (5.4 Vrms) into 4 Ohm which is 7.24 Watts and at that point the anode starts to fast approach the cathode potential and the distortion hits 0.7%. So I am enquiring about a better mains transformer to get a higher HT.

I backed it down to 5 Watts @ 0.4% distortion and went through a range of frequencies to check on the response of the amp.

30Hz = 36.1 dBm
40Hz = 36.5 dBm
50Hz = 36.8 dBm
250Hz = 37.1 dBm
flat up to : -
4000Hz = 37.2 dBm
6000Hz = 37.3 dBm
flat up to : -
18000Hz = 37.2 dBm
20000Hz = 37.2 dBm

The test set does not go above 20KHz so could not test above that and I can not get any noise floor measurements better than -36dBm which would mean at present 74.6dB down on peak output.

All in all I am pleased with how the amp is working using the EF91 and the TT15, so think I will try and make a better job of it, may even try the EF86's now I have some.

Adrian