Sourcing a PT for my upcoming Soldano SLO100 build

[Duncan]

Hey gang,

I'm about to start a Soldano SLO100 build, and I'm looking around for a power transformer. I've looked at the usual suspects (Hammond, Mercury Magnetics, O'Netics, etc.) and I think I've settled on the Hammond 290FX (640V@517mA CT, 60V bias, 6.3VAC 5.5A). I know the stock PT calls for 720V HV, but I'm wondering if 640V will have a noticeable impact to the overall tone.

I'm in Canada, which is one of the reasons why I'm leaning towards Hammond (readily available from Canadian suppliers, much cheaper than American options).

Is there anything else I should seriously consider?

[tubeswell]

I know the stock PT calls for 720V HV, but I'm wondering if 640V will have a noticeable impact to the overall tone.
...
Is there anything else I should seriously consider?

I'd start with a SLO100 schematic - which shows 497 on the 6L6 plates (ignore the pages of text at the end - that's some other idiot's stuff)

[Duncan]

I know the stock PT calls for 720V HV, but I'm wondering if 640V will have a noticeable impact to the overall tone.
...
Is there anything else I should seriously consider?

I'd start with a SLO100 schematic - which shows 497 on the 6L6 plates (ignore the pages of text at the end - that's some other idiot's stuff)

Yeah, I noticed that. I looked at the Bassman AB165 schematic, which shows 425v to the plates, and that PT doles out 660V for its HV winding. So if my mathing is correct, a 640V HV would only get me about 410V at the plates.

So I should probably find something with more gusto, it seems.

[elams1894]

I think 5.5A for the filaments may not be enough for 4x6L6 and 5x12AX7. I'd rather have about 7A minimum there.

[mresistor]

I've never heard of this company but it seems they are Soldano centric..  http://www.c3amps.com/SLO%20Transformers.html


you know the iron is going to be expensive..  I agree 5.5A 6.3vac winding is a little light for an SLO100 build

[Duncan]

I've never heard of this company but it seems they are Soldano centric..  http://www.c3amps.com/SLO%20Transformers.html


you know the iron is going to be expensive..  I agree 5.5A 6.3vac winding is a little light for an SLO100 build

Yeah those O’Netics are quickly rising as the probable winner.

There’s also Hammond’s 370 series that have caught my eye. Specifically the 373HX (https://www.hammfg.com/part/373HX)

[mresistor]

I was looking at that PT too..  nice  ..

[elams1894]

The 373HX would get you pretty close to SLO100 plate voltage spec. Heaps of filament current in reserve and you have the spare 5V winding that you could use for a relay switching PS if desired. If I were to build a SLO100, I would more than likely use this PT. I have used the Hammond 370 and 372 series for 6V6 and EL84 builds and they have performed well. Good build quality. They only get slightly warm when pushed hard. I suspect they are some-what under rated in terms of max current rating. I would not hesitate to use them again.

[Duncan]

Does anyone have any experience with EDCOR transformers? I found them via a Google search, and it looks like they've got one with 700V CT @ 400mA, 6.3VAC @ 7A.

https://edcorusa.com/products/xpwr172-700v350-0-350-400ma-100v-10ma-12v-1-5a-6-3v3-15-0-3-15-7a

[mresistor]

Lots of folks have run Edcor iron and they are high quality, I wouldn't hesitate to purchase their products.
Made in New Mexico USA,

[AlNewman]

I think 5.5A for the filaments may not be enough for 4x6L6 and 5x12AX7. I'd rather have about 7A minimum there.

The current for the little tubes is per tube, not per triode. 
So, 4 X 0.9A + 5 X 0.3A = 5.1A heater current for the 6V tap.

[AlNewman]

@elams1894 some of your builds are really interesting.  I made a point of sharing your 1 piece guitar build.  True craftmanship.

[elams1894]

@AlNewman, thanks for kind words and the share, much appreciated.

Indeed the total filament current for the SLO falls slightly under the 5.5A mark and would operate no question, however for me personally, I like to have a bit of reserve up my sleeve. OCD haunts me, and I only have myself to blame.

[AlNewman]

@elams1874, thank you for sharing.  I've been following your channel since i first saw that build, around 2016 or so?

In my opinion, the thing about transformers is you need to introduce an appropriate current in order to create an appropriate voltage.  They don't necessarily perform ideally in a situation where more is better.

[elams1894]

@AlNewman, far out, I had a look into my content folder and the LP build was 2012, jeepers, I hadn't realised its been that long.

Re: Transformer size/suitability/saturation/tone.. Thats one aspect that very much interests me. For sure, especially in guitar amps, a smaller, or undersized power transformer can contribute a significant amount to the tone of the amp as seen in many Fender amps. A very interesting topic and/or experiment indeed. Listening to comparisons between the same amp with either a monster Mercury, a ClassicTone, Hammond, and stock PT yields surprising differences in tone with the biggest not necessarily being the best. ClassicTone have always been my pick in most PT comparison blind taste tests for whatever reason. I'd love to know why and how.

Same can be said for OT's of course, where big (wide frequency range) can be a hinderance rather than a blessing. A bigger (lower) freq range OT will more easily pickup any stray hum and punish a poor layout. Whereas a smaller narrow freq range might be more appropriate to put a lead guitar in the slot. Like anything in tube amp building, everything is a compromise and a long and winding road for me.

[DummyLoad]

Use a Hammond 290HX and a FWB - It's an X mount (vertical), if you need Z mount (laydown) then use the 290HZ.

290HX Specifications



--Pete