Search found 4073 matches

by Andrew
Mon Mar 04, 2019 6:47 pm
Forum: Everyones Projects
Topic: Phono Frustration
Replies: 52
Views: 1056

Re: Phono Frustration

Dumbass me left out the battery bias on the first valve yet the voltages on it were what I was expecting. I can't quite get my head around that when G1 isn't grounded and it made sound. There's a lesson in there somewhere and it might also have something to do with why biasing can lead to microphon...
by Andrew
Sat Feb 16, 2019 10:23 am
Forum: Everyones Projects
Topic: Warning LED when valve stops conducting - a little SS help needed
Replies: 126
Views: 2557

Re: Warning LED when valve stops conducting - a little SS help needed

Can we please revisit the virtual cathodes? I see the sense and purpose of these in a AC heated circuit, turns single ended noise into common mode noise etc, but I'm not seeing the value here. The DHT heaters contribute very liitle to the noise in an amp, so there's no noise rejection benefit; there...
by Andrew
Thu Feb 14, 2019 8:28 pm
Forum: Everyones Projects
Topic: Warning LED when valve stops conducting - a little SS help needed
Replies: 126
Views: 2557

Re: Warning LED when valve stops conducting - a little SS help needed

I'm confused, to much digital stuff going on in my life at present, sorry. What does the virtual cathode circuit look like please, Mick?

A good understanding of Kirchhoff's Law doesn't do any harm here....

best regards,

Andrew
by Andrew
Wed Feb 13, 2019 3:17 pm
Forum: Everyones Projects
Topic: Warning LED when valve stops conducting - a little SS help needed
Replies: 126
Views: 2557

Re: Warning LED when valve stops conducting - a little SS help needed

Nick wrote:
Wed Feb 13, 2019 2:24 pm
Transistors never fully turn off. I would consider the resistor on the same side as the LED.
Thanks Nick, (and Mick for drawing it up) that's pretty much what I was driving at, just didn't have the time to follow it thru' the a logical conclusion .
by Andrew
Wed Feb 13, 2019 3:12 pm
Forum: Everyones Projects
Topic: DHT Heater using VCCS - PCB or Kit (Possible Group buy)
Replies: 1060
Views: 87084

Re: DHT Heater using VCCS - PCB or Kit (Possible Group buy)

A 300B driven by the small board should be fine inside a chassis, Ali, at least based upon my experience with Colin's 300B amps. I have not heard of any boards being frazzled yet, I would expect some would have reached a few thousand hours running by now. The only dead the ones so far, were the ones...
by Andrew
Tue Feb 12, 2019 7:54 pm
Forum: Everyones Projects
Topic: Warning LED when valve stops conducting - a little SS help needed
Replies: 126
Views: 2557

Re: Warning LED when valve stops conducting - a little SS help needed

The collector of the D44H11 is a clean +-ve, or on the output pin of the LD1085P, should be the same thing, if I recall correctly.

Andrew
by Andrew
Tue Feb 12, 2019 6:22 pm
Forum: Everyones Projects
Topic: Warning LED when valve stops conducting - a little SS help needed
Replies: 126
Views: 2557

Re: Warning LED when valve stops conducting - a little SS help needed

The LED shouldn't take any current when the heater is conducting, it will take a 10mA or so, when it isn't; the board's supply can deliver an amp or more...I'm not certain I see the issue, am I missing something? Equally, why couldn't the LED and driver use an external supply? Yes, as far as I can s...
by Andrew
Tue Feb 12, 2019 5:11 pm
Forum: Everyones Projects
Topic: Warning LED when valve stops conducting - a little SS help needed
Replies: 126
Views: 2557

Re: Warning LED when valve stops conducting - a little SS help needed

Thinking about this some more, I don't like the first solution at all now, I have gone off it, I would prefer something like the second, which isn't in the music signal path. Try and LED in series with 820R between the base of the D44H11 and ground and see if the LED lights up and then check if the...
by Andrew
Tue Feb 12, 2019 4:11 pm
Forum: Everyones Projects
Topic: DHT Heater using VCCS - PCB or Kit (Possible Group buy)
Replies: 1060
Views: 87084

Re: DHT Heater using VCCS - PCB or Kit (Possible Group buy)

The 1N00x diodes should be fine, can't see why not?

The correct 470K CC resistors are available from RS, does that help? I suspect the 1/2 watt ones will be fine as well, if a little over-kill.

Yep, the caps cost a fortune, pity as I just bought 24 for a a mini buy.

Andrew
by Andrew
Tue Feb 12, 2019 2:05 pm
Forum: Everyones Projects
Topic: Warning LED when valve stops conducting - a little SS help needed
Replies: 126
Views: 2557

Re: Warning LED when valve stops conducting - a little SS help needed

Thinking about this some more, I don't like the first solution at all now, I have gone off it, I would prefer something like the second, which isn't in the music signal path. Try and LED in series with 820R between the base of the D44H11 and ground and see if the LED lights up and then check if the ...
by Andrew
Tue Feb 12, 2019 1:49 pm
Forum: Everyones Projects
Topic: Warning LED when valve stops conducting - a little SS help needed
Replies: 126
Views: 2557

Re: Warning LED when valve stops conducting - a little SS help needed

I wonder if its possible to extract a signal from the heater supply when there is no heater current. That might be a useful addition to the circuit. You might be able to look and see what the op amps is doing in a "no load scenrio" and use that? Stupid question Andrew - do you mean the LM358P? Yes,...
by Andrew
Tue Feb 12, 2019 10:24 am
Forum: Everyones Projects
Topic: Warning LED when valve stops conducting - a little SS help needed
Replies: 126
Views: 2557

Re: Warning LED when valve stops conducting - a little SS help needed

Nick wrote:
Tue Feb 12, 2019 8:57 am
I wonder if its possible to extract a signal from the heater supply when there is no heater current. That might be a useful addition to the circuit.
You might be able to look and see what the op amps is doing in a "no load scenrio" and use that?
by Andrew
Sun Feb 03, 2019 4:50 pm
Forum: Everyones Projects
Topic: DHT Heater using VCCS - PCB or Kit (Possible Group buy)
Replies: 1060
Views: 87084

Re: DHT Heater using VCCS - PCB or Kit (Possible Group buy)

But seriously ( folks ) do you have a residual gripe about the GK-71 application ? - after all, it seemed to be merely a matter of feeding it with a 24V SMPS and making sure one or two caps on the board were 35V rated, as I remember ( and the heatsink up to scratch ) ? I've no gripes at all, they a...
by Andrew
Sun Feb 03, 2019 12:31 pm
Forum: Everyones Projects
Topic: DHT Heater using VCCS - PCB or Kit (Possible Group buy)
Replies: 1060
Views: 87084

Re: DHT Heater using VCCS - PCB or Kit (Possible Group buy)

pre65 wrote:
Sun Feb 03, 2019 12:29 pm
Andrew wrote:
Sun Feb 03, 2019 12:22 pm

nothing I have will do a GM70 without serious hacking.

Andrew
I thought mine were reasonably standard ? :?

GM70 & GK71 heaters the same (or very similar).
No, that's all yours and Mark's own work, Phil. I disown it. ;)
by Andrew
Sun Feb 03, 2019 12:22 pm
Forum: Everyones Projects
Topic: DHT Heater using VCCS - PCB or Kit (Possible Group buy)
Replies: 1060
Views: 87084

Re: DHT Heater using VCCS - PCB or Kit (Possible Group buy)

The "small" ones will do 300B and everything downwards, the big ones are really for 2A3, nothing I have will do a GM70 without serious hacking.

Andrew