Need help with a Radford HD 250 amplifier

gaetan8888 · 8th April 2007, 04:31 PM

Hello

I have an integrated amplifier Radford HD 250. I did replace its powers transistors and drivers.

I don't have the diagram of this amplifier, on the circuit board of the drivers and pre-driver, there is three triming potentiometers; so from the left to the right its; P6, P7 and P5. I presume that one among them is for adjusting the symmetry or for the quiescence current, but I don't know what are P6, P7 and P5 and how much millianpères is the quiescent current.

Here's a link to a photo of the circuit board of drivers and pre-driver of my Radford with the tree triming potentiometers;

http://img440.imageshack.us/img440/8...rdboardpj3.jpg

Anybody have an answer or does have the diagram of this amplifier ?

Thank you

Gaetan, Canada

Netlist · 8th April 2007, 04:38 PM

It shouldn't be too difficult to reverse engineer the board. From there I might be able to help.
Get that pencil and paper.

/Hugo

gaetan8888 · 4th July 2007, 05:59 PM

Hello

Here's some news about that Radford that I repair for a friend..

I did take, for some time, a brake from the Radford HD250 repair. And yesterday I did finish the repair.

I did found the service manual on the web.

I have used MJ15003 and MJ15004 for output, and BD139 and BD140 for drivers, there was some wrong value resistors on the board (my friend try to fix it himself), so I replaced them by the righ value.

I've put back everything and do a first test, P5 did adjust the clipping to be symmetrical.

P6 don't do very much for adjusting crossover spikes since I can't see any spike on the scope.

For the bias, I did goes first with 45 ma. for each channel, but it was sound a bit agressive, so I goes up to 75 ma bias and now it sound very good.

Gaetan

8th April 2007, 04:31 PM	#1
gaetan8888 diyAudio Member Join Date: Apr 2007	Need help with a Radford HD 250 amplifier Hello I have an integrated amplifier Radford HD 250. I did replace its powers transistors and drivers. I don't have the diagram of this amplifier, on the circuit board of the drivers and pre-driver, there is three triming potentiometers; so from the left to the right its; P6, P7 and P5. I presume that one among them is for adjusting the symmetry or for the quiescence current, but I don't know what are P6, P7 and P5 and how much millianpères is the quiescent current. Here's a link to a photo of the circuit board of drivers and pre-driver of my Radford with the tree triming potentiometers; http://img440.imageshack.us/img440/8...rdboardpj3.jpg Anybody have an answer or does have the diagram of this amplifier ? Thank you Gaetan, Canada

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8th April 2007, 04:38 PM	#2
Netlist diyAudio Moderator Emeritus Join Date: Jan 2003	It shouldn't be too difficult to reverse engineer the board. From there I might be able to help. Get that pencil and paper. /Hugo

4th July 2007, 05:59 PM	#3
gaetan8888 diyAudio Member Join Date: Apr 2007	Hello Here's some news about that Radford that I repair for a friend.. I did take, for some time, a brake from the Radford HD250 repair. And yesterday I did finish the repair. I did found the service manual on the web. I have used MJ15003 and MJ15004 for output, and BD139 and BD140 for drivers, there was some wrong value resistors on the board (my friend try to fix it himself), so I replaced them by the righ value. I've put back everything and do a first test, P5 did adjust the clipping to be symmetrical. P6 don't do very much for adjusting crossover spikes since I can't see any spike on the scope. For the bias, I did goes first with 45 ma. for each channel, but it was sound a bit agressive, so I goes up to 75 ma bias and now it sound very good. Gaetan