Radford Power Amp probs - UK Vintage Radio Repair and Restoration Discussion Forum

steepend · 21st Nov 2019, 6:04 pm

Hi,
During the early-mid 1960's i worked on the Radford account in a west end Ad agency. I was not able to afford one at the time but now in my 70's.
I now have a Radford system but my problem is that the right hand channel has gone. I've tried swapping the cables around from L to R with no joy.
Any thoughts will be appreciated. I'm a real Rookie with these things so be gentle with me !

Many Thanks

Steepend

snowman_al · 21st Nov 2019, 7:41 pm

Hi steepend,
I think this should be in the ''Vintage Audio'' section and will be moved by the Mods soon.

Please answer some questions:
Which Radford amp is it? Do you also use a Radford pre-amp?
When you swapped the cables, did you swap the inputs and then the speaker cables? Make sure you have no problem with your source / pre-amp and that both speakers are working. It is not unknown for a power amp to be blamed when the fault is in the pre-amp or a dead speaker...

Once we know which amp(s) it is we can advise on swapping the valves round from one side to another, assuming it is a valve and not transistor amp etc..
Alan

steepend · 24th Nov 2019, 12:03 pm

Hi,
Pre amp SC22, Power amp STA 25.
I swapped the cables at the back of the Speakers only...both speakers are OK.
Many Thanks
Steepend

Craig Sawyers · 24th Nov 2019, 1:56 pm

The STA25 is well thought of even today. Nice unit worth fixing.

But the fault could be in the preamp - try swapping the left and right channel connections between the pre and power. If the fault is heard on the same speaker the problem is the power amp, if it swaps speakers it is in the preamp.

Craig

GrimJosef · 24th Nov 2019, 2:57 pm

Radford used PVC-insulated stranded hookup wire in those amps. The early stuff tended to lose its plasticity if it ran warm for any length of time, which it did given that it was wired to the STAs' valveholder tags. The now stiffened wire is prone to snapping, which could explain your symptom (sudden complete loss of one channel). There are other possible explanations too of course.

Cheers,

GJ

21st Nov 2019, 6:04 pm	#1
steepend Triode Join Date: Dec 2014 Location: Petersfield, Hampshire, UK. Posts: 21	Radford Power Amp probs Hi, During the early-mid 1960's i worked on the Radford account in a west end Ad agency. I was not able to afford one at the time but now in my 70's. I now have a Radford system but my problem is that the right hand channel has gone. I've tried swapping the cables around from L to R with no joy. Any thoughts will be appreciated. I'm a real Rookie with these things so be gentle with me ! Many Thanks Steepend

21st Nov 2019, 7:41 pm	#2
snowman_al Octode Join Date: Dec 2018 Location: Llandeilo, West Wales, UK. Posts: 1,092	Re: Radford Power Amp probs Hi steepend, I think this should be in the ''Vintage Audio'' section and will be moved by the Mods soon. Please answer some questions: Which Radford amp is it? Do you also use a Radford pre-amp? When you swapped the cables, did you swap the inputs and then the speaker cables? Make sure you have no problem with your source / pre-amp and that both speakers are working. It is not unknown for a power amp to be blamed when the fault is in the pre-amp or a dead speaker... Once we know which amp(s) it is we can advise on swapping the valves round from one side to another, assuming it is a valve and not transistor amp etc.. Alan __________________ Never Leave Well Enough Alone... Last edited by snowman_al; 21st Nov 2019 at 7:50 pm.

24th Nov 2019, 12:03 pm	#3
steepend Triode Join Date: Dec 2014 Location: Petersfield, Hampshire, UK. Posts: 21	Re: Radford Power Amp probs Hi, Pre amp SC22, Power amp STA 25. I swapped the cables at the back of the Speakers only...both speakers are OK. Many Thanks Steepend

24th Nov 2019, 1:56 pm	#4
Craig Sawyers Dekatron Join Date: Nov 2010 Location: Oxford, UK. Posts: 4,984	Re: Radford Power Amp probs The STA25 is well thought of even today. Nice unit worth fixing. But the fault could be in the preamp - try swapping the left and right channel connections between the pre and power. If the fault is heard on the same speaker the problem is the power amp, if it swaps speakers it is in the preamp. Craig

24th Nov 2019, 2:57 pm	#5
GrimJosef Dekatron Join Date: Sep 2007 Location: Oxfordshire, UK. Posts: 4,311	Re: Radford Power Amp probs Radford used PVC-insulated stranded hookup wire in those amps. The early stuff tended to lose its plasticity if it ran warm for any length of time, which it did given that it was wired to the STAs' valveholder tags. The now stiffened wire is prone to snapping, which could explain your symptom (sudden complete loss of one channel). There are other possible explanations too of course. Cheers, GJ __________________ http://www.ampregen.com