Curious_George

I know for a fact that an amp can be designed as good or better than the Zen and less expensive. In triode mode, the EL84 and 6V6 are similar. You could also use a 6BQ5, but those are probably more expensive than your pedestrian 6V6. Decware has very creative marketing which has worked well for them. If I were in business making electronic products, I would be doing the same thing.

The alternate output transformers that Henry is referring to are from: https://www.musicalpowersupplies.com/products/ Current pricing is (one) $44 plus shipping. These are nearly identical to the Edcor GXSE10 watt OPT's, but less expensive. The OT10SE-HF comes in 5k & 7k primary impedance. If you want another impedance, Matt (at MPS) can wind whatever you need. Just send him an email. MPS also winds transformers for Bottlehead products, so that should give you an idea of the quality you will be getting from MPS. Great products at a great price. Lead-time is very reasonable too (right now), I ordered 4 and Matt had to make them and I received them in 10 days. OT10SE_HF_DWG_USA (2).pdf

I just compared the MPS 10 watt OPT to the Edcor 10 watt OPT. The MPS is 2.1lb, the Edcor is 1.75lb, so the MPS is slightly bigger. Overall build quality is good, but not as clean as the Edcor. The MPS transformer varnish dip is not as clean as Edcor's process. This has no bearing on performance, but is strictly an aesthetic issue. Other than that, the end bells are natural finish, not painted.

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A BOM would be a big help. If you need anything further to start the BOM, let me know. I've tried to annotate as much info on the schematic as possible. By default, I usually spec standard metal film resistors since they are the same price as carbon film nowadays. I also use Rubycon or Nichicon electrolytic caps just because of their reputation and Orange Drops for the 0.22uF/400V coupling cap.

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Pictures and more data will be posted later of the transformers.

I am familiar with George's driver board. Good stuff no doubt, but I don't like mixing SS & tube circuits unless I absolutely have too.

The Musical Power Supply Transformers came in; OT10SE-HF 5k/8 Ohm, 50mA Preliminary testing shows that they are a good transformer when used within their parameters. I tested them on a 2A3 amp biased at 55mA although 50mA is the max that Matt @ Musical Power Supply said they were designed for. More current through them will reduce the low frequency performance. 1 Watt: 40Hz @ 10% THD+N Bandwidth: 16Hz ~ 38kHz, -3dB Mid-band distortion (1kHz): 0.5% THD+N 3.5 Watt: 45Hz @ 10% THD+N Bandwidth: 20Hz ~ 38kHz, -3dB Mid-band distortion (1kHz): 5% THD+N These transformers should be good for any project that calls for 50mA or less in the output stage.

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Looks great Henry!

Great idea! You can call the amp "corazón de la música". The heart of music.

Even in (most) equipment that only has a 2-prong plug, the chassis is grounded to signal ground through a 0.1uf cap. Sometimes there is a "lift" switch for this. This allows the chassis to act as a shield (EMI/RFI) for the internal circuitry.

For those not familiar with the "Bulb Tester", it should be made with an incandescent type bulb (100W). I've never tried a newer LED type bulb, but it may work. A CFL (curly cue) will not work in this capacity.

I would add a price column just as a reference. Just so a builder knows how much an item would cost. Plus, in 20 years, we can look back and say "wow, in 2022, parts we so cheap!".

I see an HP-334 series distortion analyzer up there in the top left corner of your shelf. I have 3 that I'm not sure what to do with. There were the item to have back in the day.

That stinks. I never had any of the childhood ailments... i was like the boy in the plastic bubble. Not really, but i was a bit sheltered.

Tube gear is a lot easier to repair in my opinion. Modern solid state amps are usually direct coupled and when a transistor goes out, there is a daisy chain reaction and more transistors are damaged due to direct coupling. If a SS amp has a catastrophic failure, I'll replace all the transistors in that particular channel except for the input section but sometimes they get zapped too.

When I was designing the power supply for my 211 amp (>1kVDC), I breadboarded it as in the picture. I was careless and got bit on the hand from my finger tip out through my palm. I survived (of course), but had a nasty little puncture hole in my palm. No shocks sense then!

To continue to encourage new builders to get their feet wet, you don't necessarily need to drill holes in a chassis to get started building a tube amp; you can "breadboard" a tube amp too, as shown below. This allows you to quickly mount components and make/change connections. If wired correctly, you should not have any noise, but with a set-up like this, it is more about getting the circuit up and running.

I sent the spec to Matt.

Matt at Musical Power Supplies indicated he could wind to a specification. I have some correspondence with him, so I can contact him again. Give me the spec Cappy and I'll send it over to him.

Here is a BOM you can use for a template. Just to give you an idea. Change as desired. 300B Stereo Amp BOM_v1.0.0_010722.ods