Another Small Special build with a twist

[telentubes]

On the neg feedback in the layout, shouldn't the .1 cap be a coupling cap, and not an electrolytic?

[Synchu]

I would guess that you mean a non-polarised cap.
This is a bypass cap as part of a low pass filter.
On the schematic 0.1 is shown, but 1 uF electrolytic worked better for me and made it sound a tad brighter. it is inherently a dark amp (to my ears at least) so that was good thing, but you can certainly experiment and find out which one works best for you.
Another note on the NFB is that the 100 Ohm resistor coming from the OT secondary should be 820 at least, although both on the schematic and Morgan SW use 100 Ohm. I initially did it that way, but it dampens both the output quite significantly and (of course) the nice overdrive.
And I put the NFB on a switch

[telentubes]

Interesting about the caps. Never knew that.
Thanks for the insight on the 100R resistor. Does it need to be 5 Watts?

[Synchu]

On the resistors - that is pretty much Fender's NFB implementation (i.e. 820R and 100R to ground).
This is mentioned in Jelle's Small Special build thread as well.

I had this 5 watt'er lying around from a 5E3 build, so this was used (plus it looks cool ), but anything over and starting with 1 watt is sufficient (and even 1 watt is bit too much, but size wise it is easier to work with - at least for me).

[telentubes]

Know what you mean. A 1 Watt resistor is about as small a part as I want to work with anymore. Some of the little caps and diodes can be challenging.

[telentubes]

A little progress.
I'm getting Bournes pots from Apex, and other missing parts from Mouser and Antique Elec. Might have to condense the rectifier board (make a new one) as it doesn't lay on the side wall quite right. Ceramic caps, and E-cap for the bias yet to be added.

[PaisleyTube]

Looking excellent!

Here in Europe getting a different iron than Hammond is almost impossible (at least very expensive with shipping costs and import duties/VAT).
Or at least I don't know of any ClassicTone, Heyboer or Edcor distributors. Sowters are almost out of question price wise.

Otherwise, I think this topic is more than capable to host more than one build

Niki

Just import them yourself.

Other options: transformers from TubeAmpdoctor or TubeTown in Germany.
Maybe MarbleAmps/FNS in the Netherlands (not me).

Otherwise: try getting some 2nd hand 70s Fender iron.

I do import, use and sell MM.

[dreric]

telentubes


Nice work! Why do you have resistors in series with you diodes on the rectifier board?

[telentubes]

dreric, see this thread... https://tubeamparchive.com/viewtopic.php?t=23045

Ceramic caps need to be added as well. See the rectifier mod at turretboards.com. This is something I read about somewhere and made a drawing of. Thought I'd give it a try.

[Structo]

Not sure what is going on with the large filter caps but I use silicone RTV to glue them to the board.
Works great.

[Synchu]

telentubes - looking great!
As for the supposed switching noise with the diodes rectification - I'd just use fast switching diodes, makes for smaller rectifier board. I used UF5408 in this particular build and worked great.
I am also curious to experiment in my next build with using plain 1N4007 - what would be the effect with resistors/caps and without them.

PaisleyTube - thanks for the notes. I received a fair bit of suggestions and doubled my research efforts as well.
For import - I checked with Edcor and the shipping cost equals the cost of the transformers and I have to add VAT and customs duties as well.
There are a number of smaller companies winding transformers, such as inMADout, Welter (I think that was the name) which I will be checking, but can't find enough references on the web for these. Allparts UK site seems to have Mojo transformers available at decent cost (these are Heyboers AFAIK).
I have to e-mail TAD on who's winding the transformers for them.
I use Tube-town for most of my parts purchasing and got Hammonds there for my last low watter build. I looked at their transformers as well, but again not much of a reference on the web.
I would have been more than happy to use TRMAudio transformers for my next build, as I used them for the Small Special - very stable and great sounding units, but they don't make a 100W OT and their PT seems a bit underpowered for my purposes.
MMs are excellent, but I have to keep this budget within reasonable limit

Ughh... this ended up longer than expected, but it took a fair bit of time in the last weeks of research. However, there seems to be much more choice on the table now. Not all as cost effective as in US, but still reasonable.

[telentubes]

Tom,
The filter caps are just taped in there as spacers because I'm not yet sure if I will use just one 47uf/500V for the first stage, or two caps in parallel, or two in series.
The Sprague 20ufs are soldered in there, the others not. When it is all wired up, I'll use a bead of silicone to glue them in place.

[Structo]

Gottcha, thanks for the update.

[telentubes]

A little more progress. Waiting for the last few parts.

[Synchu]

Looks very nice!