UY85 UL84 Amplifier - Page 2 - UK Vintage Radio Repair and Restoration Discussion Forum

kalee20 · 16th Jan 2013, 1:59 pm

It is negative current feedback, taken from the cathode resistor and fed back to the input. So no it won't correct any non-linearities in the O/P transformer. Also, the damping on the loudspeaker will be nearly non-existent.

There are tone controls, but they are within the feedback loop which consequently will try to nullify them!

An interesting circuit, but not what I'd call a 'good' circuit.

Fidelity Fan · 19th Feb 2013, 10:55 pm

Back to UY85 - UL84 amplifiers - If for safety, an isolation transformer was fitted to one of these record players from which the BSR motor was also supplied, what current/VA rating would the isolation transformer need to be?

Herald1360 · 20th Feb 2013, 12:23 am

The motors don't take much power though they may need rather more VA.

Heaters are about 9W, HT maybe 12W or so, allow 25VA for the motor and a 50VA transformer should do the biz. Go for 100VA if you want it all to stay nice and cool.

Fidelity Fan · 20th Feb 2013, 5:45 pm

Ok thanks.

AC/HL · 30th Sep 2013, 7:15 pm

One post about the Radio Constructor articles moved to the Websites section for information.

16th Jan 2013, 1:59 pm	#21
kalee20 Dekatron Join Date: Feb 2007 Location: Lynton, N. Devon, UK. Posts: 5,166	Re: UY85 UL84 Amplifier It is negative current feedback, taken from the cathode resistor and fed back to the input. So no it won't correct any non-linearities in the O/P transformer. Also, the damping on the loudspeaker will be nearly non-existent. There are tone controls, but they are within the feedback loop which consequently will try to nullify them! An interesting circuit, but not what I'd call a 'good' circuit.

19th Feb 2013, 10:55 pm	#22
Fidelity Fan Hexode Join Date: Jan 2013 Location: Wigan, Lancashire, UK. Posts: 318	Re: UY85 UL84 Amplifier Back to UY85 - UL84 amplifiers - If for safety, an isolation transformer was fitted to one of these record players from which the BSR motor was also supplied, what current/VA rating would the isolation transformer need to be?

20th Feb 2013, 12:23 am	#23
Herald1360 Dekatron Join Date: Feb 2007 Location: Leominster, Herefordshire, UK. Posts: 13,708	Re: UY85 UL84 Amplifier The motors don't take much power though they may need rather more VA. Heaters are about 9W, HT maybe 12W or so, allow 25VA for the motor and a 50VA transformer should do the biz. Go for 100VA if you want it all to stay nice and cool. __________________ ....__________ ....\|____\|\|__\|__\_____ .=.\| _---\__\|__\|_---_\|. .........O..Chris....O

20th Feb 2013, 5:45 pm	#24
Fidelity Fan Hexode Join Date: Jan 2013 Location: Wigan, Lancashire, UK. Posts: 318	Re: UY85 UL84 Amplifier Ok thanks.

30th Sep 2013, 7:15 pm	#25
AC/HL Moderator Join Date: Nov 2003 Location: Heckmondwike, West Yorkshire, UK. Posts: 7,643	Re: UY85 UL84 Amplifier One post about the Radio Constructor articles moved to the Websites section for information. __________________ Bill, BVWS member