22-02-2018, 06:36 AM
(This post was last modified: 22-02-2018, 06:41 AM by Diabolical Artificer.)
Yes Jeffrey those R's look just the job, unfortunately as Mike pointed out there's a £15 surcharge. This is a big problem with Farnell, yesterday I looked at 10r MF R's, the first page of results all had the £15 surcharge ( why it costs £15 bog knows. It's £15 from Lille in Franch and the US. Digikey is only £3). So I ordered some bigger Vishay 3w's from RS and some bigger (physically) 3W's from rapid. Someone did suggest using W21's. I'll see how I go and report back.
I scoped as well as monitored voltage and current yesterday at turn on and off and at full whack. Apart from a dip of several volts at Sw off - nada. The start up is gentle, V rises over about 6 seconds due to the heaters warming up.
There is 34dB of NFB. (Hope that's right, 1v on the OP - 0.02 applied to the cathode of the IP valve so 20 log V1/V2 = 33.9.) NFB R is two 10k's in parallel = 5k and an 820p C. This isn't quite right, but ok for now. Amp is stable with a speaker load, but at some point I'm going to have to improve closed loop stability and test with a proper inductive/capacitive test load.
I'm also going to put diodes reversed biased from anode to ground to stop big inductive spikes if someone left the dummy load off by mistake sort of thing (whistling whilst looking skywards) and spikes when over driven. It can kick out 160w (36v RMS - OPT rated 120w)) without the protection circuit and has whilst fettling, gone into oscillation, but the R's in question survived this abuse. The R's have gone high whilst everything is bolted down so to speak.
A.
I scoped as well as monitored voltage and current yesterday at turn on and off and at full whack. Apart from a dip of several volts at Sw off - nada. The start up is gentle, V rises over about 6 seconds due to the heaters warming up.
There is 34dB of NFB. (Hope that's right, 1v on the OP - 0.02 applied to the cathode of the IP valve so 20 log V1/V2 = 33.9.) NFB R is two 10k's in parallel = 5k and an 820p C. This isn't quite right, but ok for now. Amp is stable with a speaker load, but at some point I'm going to have to improve closed loop stability and test with a proper inductive/capacitive test load.
I'm also going to put diodes reversed biased from anode to ground to stop big inductive spikes if someone left the dummy load off by mistake sort of thing (whistling whilst looking skywards) and spikes when over driven. It can kick out 160w (36v RMS - OPT rated 120w)) without the protection circuit and has whilst fettling, gone into oscillation, but the R's in question survived this abuse. The R's have gone high whilst everything is bolted down so to speak.
A.
