Will I have to re-bias tubes on phono-pre amp?

[geoffc]

Am pretty much a newbie to the world of tube amps so apologies in advance!

Just got myself a Yaqin MS-23b Valve Pre-Amp and am looking to upgrade the stock tubes soon with either Electro-Harmonix or JJ Electronic 12AX7's.

My question is I've read that valves sometimes need re-biasing when replaced - will this be necessary with the tubes for a phono pre-amp as I was under the impression it was only power amp tubes that needed re-biasing as pre amp tubes don't require this.

Thanks

[NRG]

Not for your pre amp and if you are keeping to the same valve type or equivalent. Bias adjustment is typically found on the output stage of a power amp but not in all cases.

[geoffc]

Thank you, much appreciated.

[PaulStewart]

Hi Geoff,

Bias won't be a problem, but in my opinion, JJs are a downgrade from a blown 60watt bulb :lol: grab youself a set of Harma retros from Watford Valve or some NOS EI's from Langrex. That is if you don't want to get some NOS GEs, which are I admit pricey these days.

Best of luck

[julesd68]

Bias won't be a problem, but in my opinion, JJs are a downgrade from a blown 60watt bulb :lol:

I'd have to disagree with this Paul ... :) When I got my old Puresound P10 phono stage it came with stock EH tubes which weren't quite doing it for me. I changed these to gold-pin JJ's on the advice of Guy Sergeant and was very happy with them - not a night and day difference but felt a bit less 'grainy'. At the modest price they sell for you can have a go and see how you get on before starting to play the NOS game ... Of course it all depends what your original stock tubes are. I messed around with NOS tubes as replacements for the stock tubes in my Conrad Johnson EV1 and only got a benefit changing the 5751 tube for a NOS 1950's GE Black Plate - kept all the others as stock ...

[PaulStewart]

Hi Jules

The problem is that for me the JJs can't take the strain when used in power amp duties and because I believe they do not have a high enough vacuum and suffer accordingly. I have never heard a JJ where I have not preferred an alternative in the same place. The lack of a proper high vacuum means they do not last as long, all things being equal to say Sovteks or Svetlanas.

As far as 12ax7s go , there are loads of good NOS tubes or for new tubes Harma retros from WV, As far as EH are concerned, this would be only one up from JJs in my opinion.