Two questions on Hackers - UK Vintage Radio Repair and Restoration Discussion Forum

Johnbarn · 24th Aug 2017, 3:39 am

I have a Mayflower 2 on which I have changed the two Hunts 0.5 uF capacitors C31,32.The set is now working very well with lovely tone. Should I change any other capacitors "just for the sake of it" or leave well enough alone? There are two other Hunts capacitors of similar construction but different value.
Secondly on my Sovereign 2 I recently replaced both PP9 batteries because they were causing drop off in performance. New batteries cured this but I was surprised to find that while one of the old batteries was reading 5.5 v on my Avo8 the other was still reading 8.5 v. How can this be when both are in series?

Nuvistor · 24th Aug 2017, 7:45 am

The PP9's, if they are the same make they are probably from a different batch, I have had similar occurrences with C type cells in radios, one cell down much further than the others.

The two Hunts capacitors, if they are the easy to change I would normally replace them, which ones are they?

Frank

stevehertz · 24th Aug 2017, 8:09 am

Not sure why you seem to suggest that their voltages should have been equally maintained better as they were connected in series? I'm not convinced that it makes much difference either way (it's down to the 'quality' of the individual battery isn't it?) but hypothetically speaking surely if they were connected in parallel it would help the voltages remain similar better?

'LIVEWIRE?' · 24th Aug 2017, 8:25 am

The difference battery voltage is most likely due to differing internal resistances of the two batteries. A PP9 (or any other 9v battery) is made up of 6 nominally 1.5v cells. If one or more of these cells is below standard it will have a higher internal resistance to the others

Johnbarn · 25th Aug 2017, 11:23 pm

Thank you for the replies. Both PP9s were Ever Ready Silver, same date and from same batch but I suppose the internal resistance is the key and could be different. Frank, the two Mayflower caps which I might consider changing are both yellow Hunts type - C21 and C42, both 0.1uf, but the service manual doesn't give any indication of them causing problems unlike the ones I have replaced, C31 C32 grid couplers which are known to cause distortion. Tempted to leave well enough alone in the meantime. John n

24th Aug 2017, 3:39 am	#1
Johnbarn Pentode Join Date: Feb 2015 Location: Belfast, Northern Ireland, UK. Posts: 130	Two questions on Hackers I have a Mayflower 2 on which I have changed the two Hunts 0.5 uF capacitors C31,32.The set is now working very well with lovely tone. Should I change any other capacitors "just for the sake of it" or leave well enough alone? There are two other Hunts capacitors of similar construction but different value. Secondly on my Sovereign 2 I recently replaced both PP9 batteries because they were causing drop off in performance. New batteries cured this but I was surprised to find that while one of the old batteries was reading 5.5 v on my Avo8 the other was still reading 8.5 v. How can this be when both are in series?

24th Aug 2017, 7:45 am	#2
Nuvistor Dekatron Join Date: Aug 2013 Location: Wigan, Greater Manchester, UK. Posts: 9,433	Re: Two questions on Hackers The PP9's, if they are the same make they are probably from a different batch, I have had similar occurrences with C type cells in radios, one cell down much further than the others. The two Hunts capacitors, if they are the easy to change I would normally replace them, which ones are they? Frank

24th Aug 2017, 8:09 am	#3
stevehertz Dekatron Join Date: Sep 2011 Location: Rugeley, Staffordshire, UK. Posts: 8,834	Re: Two questions on Hackers Not sure why you seem to suggest that their voltages should have been equally maintained better as they were connected in series? I'm not convinced that it makes much difference either way (it's down to the 'quality' of the individual battery isn't it?) but hypothetically speaking surely if they were connected in parallel it would help the voltages remain similar better? __________________ A digital radio is the latest thing, but a vintage wireless is forever..

24th Aug 2017, 8:25 am	#4
'LIVEWIRE?' Rest in Peace Join Date: Mar 2006 Location: N.W. Oxfordshire(Chipping Norton) Posts: 7,306	Re: Two questions on Hackers The difference battery voltage is most likely due to differing internal resistances of the two batteries. A PP9 (or any other 9v battery) is made up of 6 nominally 1.5v cells. If one or more of these cells is below standard it will have a higher internal resistance to the others

25th Aug 2017, 11:23 pm	#5
Johnbarn Pentode Join Date: Feb 2015 Location: Belfast, Northern Ireland, UK. Posts: 130	Re: Two questions on Hackers Thank you for the replies. Both PP9s were Ever Ready Silver, same date and from same batch but I suppose the internal resistance is the key and could be different. Frank, the two Mayflower caps which I might consider changing are both yellow Hunts type - C21 and C42, both 0.1uf, but the service manual doesn't give any indication of them causing problems unlike the ones I have replaced, C31 C32 grid couplers which are known to cause distortion. Tempted to leave well enough alone in the meantime. John n