KEL84 advice -please...

[Bonky]

Thanks Bob and Phil; understood.

BW

Richard

[vinylspinner]

Hello Richard,

The KEL84 is a lovely amp, it was the amp that got me into valves big time.
I’m sure that you will enjoy the build experience and have a nice sounding amplifier at the finish, wish I had kept mine.

Nigel

[bob orbell]

Something I feel I should add for Bonky, is in the kit, you will have black headed 3 mm screws, these may be Phillips or Pozi drive, please make sure you use the correct driver, as there is not a universal driver, and the wrong driver will f88k the heads up making the screw look like ****, . BOB

[Bonky]

Originally Posted by bob orbell

Something I feel I should add for Bonky, is in the kit, you will have black headed 3 mm screws, these may be Phillips or Pozi drive, please make sure you use the correct driver, as there is not a universal driver, and the wrong driver will f88k the heads up making the screw look like ****, . BOB

Thanks Bob, I've got some....somewhere....


Richard

[Richard]

Yes if the voltages check ok it should be fine. Remember to connect 8 ohm resistors or old speakers to each channel before firing up without any input signal. The inputs are best shorted with shorted RCA plugs or by connecting to a CDp or similar source without it being switched on. (Some amps will react to local RF interference picked up on open inputs.)

It's easy enough to do some basic checks with the sig gen and scope later if you want. Hook up sig gen > KEL84 > scope with 8R load resistors in place. Wind up the sig level to give 8V p-p on the scope at 1KHz. This is your 1W reference point. Sweep frequency looking for a flat response on the scope with a roll off either end of the audio bandwidth. You can also check SW response usually at 1KHz and sweep power response

[Bonky]

Originally Posted by Richard

Yes if the voltages check ok it should be fine. Remember to connect 8 ohm resistors or old speakers to each channel before firing up without any input signal. The inputs are best shorted with shorted RCA plugs or by connecting to a CDp or similar source without it being switched on. (Some amps will react to local RF interference picked up on open inputs.)

It's easy enough to do some basic checks with the sig gen and scope later if you want. Hook up sig gen > KEL84 > scope with 8R load resistors in place. Wind up the sig level to give 8V p-p on the scope at 1KHz. This is your 1W reference point. Sweep frequency looking for a flat response on the scope with a roll off either end of the audio bandwidth. You can also check SW response usually at 1KHz and sweep power response

That's very useful; thanks. What wattage of 8 ohm resistors would you advise?

I may need to ask again about using the 'scope and SG (!)

BW

Richard

[bob orbell]

The amp you have chosen is only 12 watt, but I would recommend 50 watt mounted on a aluminium heat sink, if at a later date you wish to do a full power test, even the wattage I have mentioned will get bloody hot, as for the scope, to be honest, if you are not savy with it, you may not know what you are looking at on the screen, my advice again, is build it, test as instructed, if all is well connect up and listen, then, try and find someone who can show you how to use the scope, you can learn a lot from watching and talking to a competent electronic engineer, but as has been mentioned, the scope comes in to its own for most fault finding, I should think that 90% or more of our members do not posses, or no how to use a scope, as has also been mentioned, a good multi meter is very useful if not essential. Have fun. BOB

[Bonky]

Originally Posted by bob orbell

The amp you have chosen is only 12 watt, but I would recommend 50 watt mounted on a aluminium heat sink, if at a later date you wish to do a full power test, even the wattage I have mentioned will get bloody hot, as for the scope, to be honest, if you are not savy with it, you may not know what you are looking at on the screen, my advice again, is build it, test as instructed, if all is well connect up and listen, then, try and find someone who can show you how to use the scope, you can learn a lot from watching and talking to a competent electronic engineer, but as has been mentioned, the scope comes in to its own for most fault finding, I should think that 90% or more of our members do not posses, or no how to use a scope, as has also been mentioned, a good multi meter is very useful if not essential. Have fun. BOB

Thanks again Bob.

Edit: Do you mean something like this: https://uk.rs-online.com/web/p/throu...stors/8459996/

?

BW

Richard.

[bob orbell]

Yes, that is what I have, do you have an account with RS ?, I think that you need to spend so much unless you do, I have an account and will get them for you if you ask. BOB

[Richard]

Originally Posted by Bonky

That's very useful; thanks. What wattage of 8 ohm resistors would you advise?

I may need to ask again about using the 'scope and SG (!)

BW

Richard

Yes indeed, as Bob says for power testing, though you can use much lower rating 7W or 10W 6R8 or 8R2 etc from Maplins for a few pence for checking through voltages after the build. Easiest way to get familiar with the sig gen and scope is to hook them together directly and have a play with the various controls