Amp initial testing.

pre65 · Post by **pre65** » Fri Sep 21, 2007 3:39 pm

Hi-temporary bases now fitted,and ready for the contest.

http://i111.photobucket.com/albums/n146 ... hed001.jpg

pre65 · Post by **pre65** » Mon Sep 24, 2007 11:06 pm

Hi-it was suggested at Witham that the gridstopper resistors on the C3g (PT15 amp) which are 150R carbons might be better replaced by higher values.

BUT i cant remember what value (s) were reccommended !

Can anyone jog my Wobbled memory please ?

Post by **Nick** » Mon Sep 24, 2007 11:42 pm

I would try 1k. The c3g has a input cap in the <10pf area, so thats still only a roll off in the order of >15MhZ, so its not a case of hurting the top end of the music.

pre65 · Post by **pre65** » Mon Sep 24, 2007 11:51 pm

Thanks Nick.

Now i know carbons are the way to go (but dont know why) and i have some 1K metal films in my parts box.

Is this a no no ?

Post by **Nick** » Tue Sep 25, 2007 7:46 am

pre65 wrote:i have some 1K metal films in my parts box.

Metal film, resistors consist of a ceramic tube with the metal on the surface, the resistance is increases by curring a spiral in the surface to increase the effective length. This will increase inductance. which could do more harm than good on the grid of the pentode, as instead of just damping the thing, it will cause a LC circuit possibly increasing the chance of instability.

That what the stopper needs to be as close as possible, the connecting lead also has inductance that will promote resonance.

pre65 · Post by **pre65** » Sat Nov 17, 2007 10:13 am

Hi-i want to test the power supply for "Chokeoskvi" but i have not got the amp yet.

So i thought i would use a load resistor as a substitute but my maths,and ohms law is very rusty.

So i will have a go.

Specifications are for 180V and according to James D the circuit draws 43ma so is it a simple calculation

R = E/I

which is R = 180/0.043 = 4186 ohms

Then i suppose i need a resistor power rating

P =I squared X R

P = 0.043 X 0.043 X 4186 = 7.74 Watts

Have i done it right ???

Post by **Nick** » Sat Nov 17, 2007 12:28 pm

Yep, looks perfectly correct to me.

pre65 · Post by **pre65** » Mon Nov 19, 2007 1:02 pm

Hi-i could not find anything in my resistor box suitable for using as the load (spent ages with a parallel resistor calculator)so i have taken the plunge and fired it up anyway.

No dramas,smoke etc-just 4 nicely glowing 6D22S rectumfriers.

The off load output voltage seems to have settled at 277V.

pre65 · Post by **pre65** » Mon Nov 26, 2007 2:18 pm

Hi-on the power supply for "Chokeoskvi" i have the IEC earth to chassis,and the centre taps for the HT and heater connections going to a star tag,one for each channel.

All the other earths also go to this "star" and when tested on its own (and with a dummy load) everything seemed ok.

Now today whilst checking everything twice before connecting the monoblocks i realised that i had not connected the "star" to chassis earth,so i clipped a lead in and as soon as i switch on it trips the main household circuit breaker !

So what might i have dun wrong ?

I have sat and thought about it but have drawn a blank.(no supprise really.)

pre65 · Post by **pre65** » Mon Nov 26, 2007 3:00 pm

Hi-i have looked again,and i have found my error.

I HAD CONNECTED THE PRIMARY CENTRE TAP TO THE STAR AS WELL !!

I cant believe i did that.

Post by **Nick** » Mon Nov 26, 2007 3:04 pm

Does the incoming L+N go to anything other than the transformer primary?

Is there anything else thats connected to the chasse?

I would guess it means there is a wiring fault somewhere, but just what is the problem of course.

You could try disconnecting the link to the star earth, and with the amp on, measure the voltage between the star and earth, that might give you a clue. But assume the chassis and everything in it is a B+ potential for the moment (ie don't touch).

audio-talk

Amp initial testing.

#61

#62

#63

#64

#65

#66

#67

#68

#69

#70

#71