5E3 1st build/ general dumb Qs

[The Captain]

Hi- if anyone can shed any light here, as Im ordering separate bits for a 1st 5E3 scratch build..

1. I can only get 25uf (3x on board electrolytics) 25v here in uk: its always 50v on schematics etc-- is 25v ok?
2. Eyelet/ circuit boards (on kit pics for eg) seem to show a 2nd identical sized board tucked behind the main one --is this right, if so whats it for?
3. I can't find details of the cabinet cut-out dimensions for the chassis.. iirc its 12.5" long, but the width?
4. As a general rule, do trannies come with mounting screws/ nuts?

Much appreciate any replies, Captain.

[MWJB]

1. 25v is OK for the 25ufs on the preamp tubes, use a 50v or better cap for the power tube's cathode bypass cap.

2. If you order a 5E3 paper style eyelet board it should come with a 2nd blank board. This blank inslulates the voltage carrying components on the top board from being grounded by the chassis.

3. Usually by a couple of self tapping screws. There are holes in the chassis, just make sure that they line up with those in the boards before you start loading up with components.

4. Not that hefty but some better quality kits provide an additonal bracket mounted on the PT as additional support. Can't remember if they're #6 or #8 on the 5E3...they cost pennies so splash out on 2 of each plus keps nuts.

5. PT's (assuming that you are using the original style) are lay down style and the bolts that hold the PT together double up as mounting bolts. OTs (and stand up PTs) can be mounted with self tappers/nuts & bolts as appropriate. Hoffmanamps.com has a good nuts/bolts/screws page and can turn round small parts to the UK as quickly as most UK companies (also check out his grounding diagram).

Lastly, and I'm not trying to be unkind, from the questions you ask, I'm not sure that scratch building an amp, without proper support, is within your capabilities right now. The 5E3 is pretty well the fewest number of parts to acheive push-pull operation, but, it is naive to think of building one as "simple". Lots of pitfalls re. layout, lead dress and parasitic occilations.

Having said that, everyone starts somewhere so get lots of pictures of 5E3s, study them with the layout, until you know where everything needs to go before you start soldering (how's your soldering technique?). When you do start, triple check every connection, marking them off the layout as you go.

TAD have a step by step champ build on their site, it will give you some idea of the order of assembly.

Read up on safe practices, in fact I would suggest enlisting the help of an experienced tech (I'm 100 miles away from Stratford if you can't find anyone nearer) when you come to powering up...don't do it by yourself, no matter how tempted you are (a big flash, puff of smoke and all your hard work down the drain?).

Keep asking questions whenever you are not sure about something, no matter how "dumb" you think they might be (photos of work so far would be handy with any queries). Wait for responses before continuing. People here can decide whether they want to get involved or not and when it comes to safety I'm sure we would be happy to stop you damaging your amp/yourself.

[MWJB]

Sorry, got out of synch with your Q no's - Re. the chassis cut out, wait til you get the chassis and then work from that.

[Bruce / Mission Amps]

Hi- if anyone can shed any light here, as Im ordering separate bits for a 1st 5E3 scratch build..

1. I can only get 25uf (3x on board electrolytics) 25v here in uk: its always 50v on schematics etc-- is 25v ok?

2. Eyelet/ circuit boards (on kit pics for eg) seem to show a 2nd identical sized board tucked behind the main one --is this right, if so whats it for?

3. I can't find details of the cabinet cut-out dimensions for the chassis.. iirc its 12.5" long, but the width?

4. As a general rule, do trannies come with mounting screws/ nuts?

Much appreciate any replies, Captain.

1. 25v is OK on every preamp tube cathode bypass cap in this amp except the 6V6s, which, although seldom run more then about 22vdc, should probably have a 50v-100v cap.

2. Insulation... the bottom of the eyelet board has quite a few of bare wire tips and exposed solder joints. These can short out to the grounded chassis if not insulated from the chassis.

3. I get asked this all the time and it is amazing to me because the 5E3 chassis dimensions have been posted all over the Net for a couple years.
Chassis dimensions vary a bit by vendor but the average size is:
14.5" left to right and 2.625" X 4.0625".

4. They will come with the screws and nuts that hold the laminations together but usually not the nuts that hold the transformer into the chassis.
Standard size is 8-32.

[The Captain]

Thanks a bundle for these replies.. some very good advice from MJWB and Bruce here. I understand the 2nd "isolating" board now- I planned to use stand-offs anyway for same theory. Ill ask Barry at Ampmaker specifically for at least 1 50v 25uf cap if he can supply (odd how I cant find any), & wait to cut a cab slot when I have the chassis here.

Sensible queries regarding my level of skill etc MJWB: it is a step up for me to try this for sure, tho I have modded hifi preamps & built a psu (admittedly not at such voltages), and had my 1st step/ practice modding a Valve Junior amp for this as it were. So although Im still a relative fresher, with care etc... There's much info on the net as much as (if not more, most of which Ive researched) the instructions that'd be supplied with a 5E3 kit it seems. I had the idea that once built and 3x checked (polarity/ layout/ wiring etc), Id take it to someone more experienced for the powered checks: if I may MJWB, and can't find someone closer by, I might take yourself up on the kind offer.

Cheers folks, Captain.

[MWJB]

Derek at Watfordvalves.com usually has Sprague 25uf 50v, but 22uf at 63v is more commonly available in the UK (most folks in the trade get them from rswww.com) and will do the trick, if no luck at Ampmaker try Barry Vyse at torresamps.com in Pinner.

Re. powering up - you'd be welcome to.

Cheers, Mark.