300b clone

Hi all, I'm the proud new owner of Clive's WAD 300b clone, hopefully I can do it justice!

I managed a quick glance at things last night and just wondered which caps are recommended for C9/C10. Clive kindly passed on the spreadsheet detailing the components and what was used, any further thoughts on this would be great!

Stu

[KennyK]

best of luck Stu.
I really wanted to give this one a go, but felt it was just a bit beyond me at the moment.

keep us posted.

[Greg.]

Hi Stu,

I and others from the original clone posse used aluminium electrolytic, 450V, 330uF by Evox Rifa. They are low ESR. RS part no. 434-0986. Not cheap though. You won't get much change out of £20.

What are you going to use for C11/12? I suggest motor run caps. 20uF will be fine. Alternative is some oil filled jobs from Michael Percy in the States.

Best wishes,

Greg

Hi Greg,

I did notice those Evox last night so will be going for them. The C11/12 question was raised this morning as I pondered things over a cuppa, a (very) quick look through CPC and RS didnt come up with much but I did notice Rapid Electronics had a couple of motor run caps but I've not studied these in any depth. If you've any suggestions please feel free. BTW, Clive's given me plenty of reading matter but I may be short of a couple of things. The main one is the details for the revised psu pcb, I have some details with your name on but no details etc, and as yet I cant quite figure it out fully. If you've any details on this Id be very grateful.

Thanks Kenny, this is my first power amp build from scratch. I do have experience with power amps though and Ive made quite a few phono's, pre's filter's etc. Even so, I feel Im going to need the expertise of this board. BTW, good luck with the EL84.

[Clive]

Hi Stu,

The psu board has the standard psu on it, I think it may be inverted compared to the original. It has in addition the dc power supply for the two small valves. The circuit for this is I think stapled to the back of the instructions. You need to check you get the grounds right when using the dc heater supply. I remember somehting about removing a ground connection from the main pcb.

I was considering not using the psu board, I was going to mount the rectifier on a sub-chassis plate. The rectifier socket would have 8 pins but of course only 4 are used, this is enough to be able to mount the diodes on the pins and take leads to the filter caps. I would then have used a small tag board to mount the dc supply for the small valves. This way there would be more room in the chassis and the rectifier would be more accessible. Just my preference, you have the choice to use the pcb or not.

Don't worry, it'll all become clearer when you're studied it for hours....

Cheers,

Clive

Hi Clive,

Interesting idea, I'll shall study that in some depth later, you might have something there, hmmm you've got me thinking (always dangerous, I wont tell you what happened the last time I thought about something, luckily the judge was sympathetic). I shall ponder some more..........

[Greg.]

Hi Stu,

I've been giving your project some thought. I believe I forwarded to Clive all the documentation I have so hopefully he has sent it onto you.

Yes, we did mess about with the PSU board. On the original WAD kit, C9/10 were smaller and not of the higher quality the ones I've recommended are. On the original, the PSU board was mounted on long stand-offs so that the GZ37 was countersunk into the top of the chassis with the edge of the glass envelope of the rectifier flush with the surface of the chassis. This matched the mounting of the 300B's, and IMHO, makes the whole amp more aesthetically pleasing to the eye. C9/10 were originally mounted between the board and the underside of the chassis top plate. To use the Evox-Rifa's we hoped to suspend the components in the same way as they are on the amp board, so as Clive correctly states, we inverted the circuit board to achieve this. Unfortunately there was still insufficient room to mount C9/10 directly onto the board so I reverted to mounting them with capacitor clips off board and using the original mounting positions on the board for respective by-pass caps. If you don't want to countersink the GZ37, space as I describe will not be an issue. As suggested, motor run polypropelene caps will be fine for C11/12. They mount on clips and protrude through the chassis top either side of the mains Tx. Typical candidates are the LCR's supplied by Maplins, part no RG68Y. As with other caps of this type, there is a mounting stud on the end which needs to be cut of for appearance sake. Being plastic (others are often metal and harder to deal with), this is easy to do, surface fill with some body filler, polish and spray paint with an oil based paint (Humbrol) that won't compromise the plastic cap case.

As Clive says, the DC heating circuit for the driver valves is incorporated onto the side of the PSU board. You don't need to use this. You can do it as Clive suggests or even stick with the original AC heating.

You are at a bit of a disadvantage because when the five of us built ours, we were constantly consulting each other on issues that presented. As you say, although a clone, this is effectively a scratch build.

If you PM me your phone number, I'll be happy to talk anything through with you and can check if there is any other printed matter I could send you to help. Likewise, if you send your email, I'll send you a spread sheet detailing specifically the components we selected for our builds.

Best wishes,

Greg

[Clive]

Hi Stu,

Greg's info is good, as I would expect!

You should have all the info Greg sent me, including the spreadsheet but if you are missing anything hopefully Greg can assist. Since Greg sent the info I had a hard drive crash but as hi-fi is so important I'd backed up these files. I believe you have all the info.

Greg and myself have a different view as to what looks right. He prefers valves to have the the bottom of their envelopes flush with the chassis. I prefer the base to to proud of the chassis - form follows function. You choose, it's just a few spacers between fellow BB members.

Cheers,

Clive

[Paul Barker]

Well I think you should have a cat fight.

[Clive]

Originally Posted by Paul Barker

Well I think you should have a cat fight.

Meow, nah if Greg has a combi you are welcome to discuss but 1 to 2cm on valve height isn't a big deal.