Croft Epoch & the 5691 valve

[Wakefield Turntables]

After much tube rolling I've decided that this is the best valve that I've heard in my system. At the moment the Epoch is designed just to take a straight 6SL7 valve but the 5691 is designed to be a premium version of the 6SL7 so my question is do I need to do any additional mods to the Croft to get the most out of the 5691 valve? I can't see myself moving away from the 5691 variants, I may at some point in the future want to try some Mullard ECC35's but in all honesty I'd be perfectly happy to stick with the 5691.

Thanks

A

[Audio Al]

Email Glen

[Wakefield Turntables]

Yes I've done that but it's always nice to hear what other people think and it allows me to review my options. ;)

[Firebottle]

It's a perfect drop in, except ... the heater current is twice that of the 6SL7.

The heater circuit may not be up to the rating, check first.

[Wakefield Turntables]

Well I've got three of the buggers playing away at the moment and apart from a little extra hum everything seems ok.

[Primalsea]

When you say hum is it from the speakers or mechanical hum from the transformer? If its mechanical hum this could be down to too much current being pulled through the transformer, ie. it is being stressed due to overload.

[Wakefield Turntables]

Not sure TBH. The Tannoys have always demonstrated some hum (what I thought was transformer) even when using bog standard 6SL7's. Paul, thanks very much for pointing this out. I've emailed Glenn so I would hope that he can explain further, we shall see! I've done that much valve rolling I thought that I might have loosened one of the resistors in the amp, it's always on the left channel (as I sit down).

[Primalsea]

Not sure TBH. The Tannoys have always demonstrated some hum (what I thought was transformer) even when using bog standard 6SL7's. Paul, thanks very much for pointing this out. I've emailed Glenn so I would hope that he can explain further, we shall see! I've done that much valve rolling I thought that I might have loosened one of the resistors in the amp, it's always on the left channel (as I sit down).

I think you maybe confusing power supply hum, the 50hz hum you can hear coming from the speakers, with mechanical transformer hum. Mechanical hum is the actual transformer vibrating so much that you can actually hear it quite clearly. All transformers hum a little bit but if overloaded they hum a lot more. The hum will be from the actual piece of equipment, not the speakers.

If you can only hear some increased hum from the speakers this is generally due to the modification drawing more current than what was originally designed, but generally not enough additional to cause a problem, other than just an increase in the noise floor.

[Wakefield Turntables]

No, the Tannoys dont hum (my mistake, sorry). I've done a little experimentation and I know full well that the left channel on my pre or power amp hums a little more than the right. I guess I'm spoiled a little in having a solid state setup that has no hum and a very very low sound floor. I'm looking into changing my equipment setup and my racks to minimise vibration getting into my TT.

[Primalsea]

Okay, sounds like it could be that you have a minor ground loop or something just causing less power supply noise rejection in one channel somewhere. If there is no extra noise or excessive heat the power supply must be very robust and over-specified to handle a 2 times increase in current draw on the heater supply.