E288C Valve

[Spectral Morn]

HI Mike


Yes no problem i will do it tomorrow I am off to bed now...


Regards D S D L

[Spectral Morn]

Photos of the Music Reference 200 amplifier...sorry these are not better lights poor here today. The fuse above the empty socket was blown. I am amazed the amplifier was still going and making great music from only one valve on that channel. Until I noticed the blown valve glowing bright blue around its bottom inside the glass, you would not have known anything was wrong. Roger M the designer claims bomb proof operation for his kit...seems to be true on this showing.

Front of amplifier



Close up of bias holeappears to be adjusted via slot screw driver.



Rear of amplifier with tp points ? I assume these are for connecting your DVM during the bias process.



Long shot with writing about bias ratings 40mv +or- 4mv.



This should help. Can you give me exact instructions of what to do ? Thanks. Is it not odd to have only one bias adjusting port. How do you adjust for both valves on each channel, is it done individually, or is it done with them being a pair ? Hence there only being one bias trim adjuster thingy . I would have thought if you set one then do the other by moving the same trim pot, you would stuff the setting for the valve you have just done. Or does this just allow you to check how each valve is reading.

I am getting some valves off Marco....


Regards D S D L

[Ali Tait]

Ok Neil,not knowing your amp or being familiar with the circuit,I would suggest you need to do the following-On the rear of the amp you have two "TP" sockets on each channel.Connect your meter leads between each channel's TP socket and it's nearest 8-ohm speaker socket i.e. one lead to TP,one to the nearest speaker socket.It doesn't matter which way round,you may just get a negative reading instead of a positive on the meter,this does not matter.Given that you only have one bias pot per channel,I would say you need to switch between both "TP" points on each channel (and it's nearest 8-ohm speaker socket) and twiddle the bias pot with a screwdriver so the readings you get are as near to 40mV and also each other as you can get on each channel.You may not be able to get quite the same reading on each channel,but don't worry about that.If they are quite far out,try swapping the valve pairs in each channel about till you get a good combination that measures as near as you can get them.Don't be anal about it though,near enough really is good enough! Does this make sense? Don't hesitate to ask if you're not sure.

[Spectral Morn]

Hi Ali

Yes thats what I thought but if in doubt always ask.... You must have the speakers attached, so the outputs are under load as well YES/NO and let the amp warm up a bit before doing the test....how long ? Then check again a bit latter.

Is that right.

I used to own a T+A V10 amp, but the bias was set via a built in meter. The access was terrible from holes under the amp. Who thought that was a clever thing . You had to lift it up (as the access holes where right in the middle of the bottom). I took the top shelf off my table and did it that way but what a real pain. Other than that the valve tester,valve life clock and bias reducer were great ideas all at the push of a button, with a built in screen idiot proof. Sound was good but veiled. Oh yes the fan in the bottom was to loud the other reason why I sold it on. Beautiful looking amp though.




Regards D S D L

[Ali Tait]

I assume this is a push-pull amp yes? In that case,yes DO NOT run the amp without speakers connected,as they form part of the circuit,and you may fry the output transformers if you do so.In similar situations I have (assuming you use banana plugs) plugged the speaker leads in so they just make contact,leaving a little bare banana plug hanging out of the end of the socket,so you can connect your DMM lead to this with a crocodile clip (if you have some!) Failing that,unscrew the nut on the speaker socket to expose the hole drilled through.Plug your DMM lead into this and then tighten down the nut.Then plug your speaker lead in as far as it will go.As for the amp being warm,give it a few minutes before the first reading,then just turn it on and off to get the others once it's warmed up a bit.Croc clips would make the job a lot easier as you could just leave the amp on as you swap the leads around.This is quite safe to do,just try not to burn yourself on the output valves!

[Spectral Morn]

Thanks for the help Ali

I will let you know how I get on when the valves I have ordered today come.



Regards D S D L

[Mike]

Ah... jolly good!

Ali beat me to it again. All sorted then Neil?

[Ali Tait]

No worries,glad I could help.

[Spectral Morn]

Thanks for the help Ali and Mike.


I may have questions but I wont know until the valves I have ordered, come next week...Marco came to my rescue,TOP BLOKE


Regards D S D L

[Ali Tait]

Nice one.Let us know how you get on.