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The power supplies you describe sound like an interesting option, especially if their MTBF proves to be up to the challenge. SMPSs tend to be small and light enough that installing two with a failsafe relay is another option. Please keep in mind that not all relay circuits are "klugy", and relays properly chosen for the application can have very impressive reliability figures, as borne out by their continued use in many industrial settings. Also note that the two-component relay-based warmup circuit I described is actually quite elegant: if the relay fails in any way (open coil or faulty contacts), the circuit will continue to pass current to the filaments. The components get ungainly in a big amp, but in a 12V string in a smaller amp that circuit is a good solution.

You're very welcome.

I'm very glad you enjoyed it!

Thanks very much for your kind comment!

Thank you very much for the high praise.

Generally, a tube going microphonic is not a bellwether for a pending catastrophic failure. There are many advocates of replacing all output tubes simultaneously (and using matched pairs or quads), but there's nothing wrong with replacing a single output tube, especially if you're happy with the amp's sound. As I mentioned in the video, you might even prefer a slight mismatch. One caveat: if the amp is being used on tour, then I would recommend swapping out all output tubes at once with a set that has been pre-tested in order to weed out infant mortality. Otherwise, play, enjoy, and save your hard-earned dough.

@@q.b.amplification8056 Thanks very much! As long as it won't harm the amp, then I'll try swapping out the one valve and see if that has any effect, negative or positive.

The Solitaire's DI output comes after the push-pull output stage - including the output transformer and reactive load. The idea was to replicate as closely as possible to the signal chain of a mic'd tube amp.

Thanks very much for your comment. I avoided that can of worms because it's hard to stem the tide of widespread beliefs that are demonstrably untrue. The only meaningful way to compare signal caps is to A/B them in real time - blind. That means not knowing which cap is selected when evaluating its sound. And both caps should have the identical measured capacitance. This kind of comprehensive testing is virtually never performed, but if it was, there would be a lot of embarrassed people who were previously convinced of the nature of perceived differences between capacitors. It's hard for people to accept their own natural tendency to imagine hearing things that aren't there rather than appear ignorant or insensitive. It would be revealing to set up an A/B test with identical caps painted different colors. You can bet your bottom dollar that the orange ones would sound harsh to most listeners who knew they were in circuit compared to the cream-colored ones.

@@auburnamplifiers1786 Guitar players are notorious for listening with our eyes.

@@auburnamplifiers1786Shhhh I sell vintage Bumblebee and Black Beauty caps for $40 each. They can sniff the cork while I drink the wine lol.

Thanks very much. A lot of work went into developing the Solitaire.

Nice to hear. Many thanks.

Made me smile. Thanks for that. :)

After reading your comment, I again checked for data and research regarding the relationship between tube filament voltage and longevity, but I couldn't find anything authoritative that supported your viewpoint. One paper found that running 6.3V filaments at 6.1V extended their life by 50%. Transmitter maintenance personnel often run new tubes at slightly higher than their rated filament voltage, then back it off to a slightly lower than nominal voltage to maximize their life. Keep in mind that 6.0V is less than 5% lower than 6.3V, and that filaments fed by a power transformer winding typically see much wider voltage deviations due to normal variations in the mains voltage (6 to 10%), historical changes in the mains voltage (5 to 10%), and normal variations in transformer windings. Also keep in mind that filament failure is a relatively minor cause of overall tube failures. Of course, there's no harm at all a running audio amplifier tube filaments at precisely 6.3 or 12.6V (and fully current regulated) if you can find a way to do that, but in practical applications this pursuit would soon give way to diminishing returns.

They're built to order exclusively from auburnamps.com. You choose your options and we email you a delivery date. We take a refundable deposit while we're building your amp, which typically takes several weeks depending on components inventory. When it's ready, you pay the balance and we send you your new amp. You have 30 days to evaluate it with your own instruments and rigs. If you're unhappy with it for any reason, you can send it back to us clean and we give you a full refund. We've never had one come back.

@@q.b.amplification8056 Thanks!

Thanks for that. We'd love for you to try one. We don't post sound clips because we honestly don't think they're an effective way to evaluate gear. You don't know how the clips were recorded or produced, we don't know how they're being listened to, and they can't represent you playing your instrument anyway. Instead, we let you live with your Auburn for a month. If you're not completely happy with it, just send it back clean and we refund your money. This goes for our made-to-order amps too. In 12 years, no one has ever taken us up on it.

Thank very much for your insights and kind praise, John. It sounds like you and I have had similar careers. I hear you about slide switches in general, and we made our decision to go with them on the Solitaire only after careful consideration and finding very good ones (we shortlisted three brands and tested them all). We wanted a low-profile switch because we figured most users would find a tone stack setting they liked and rarely change it, at least for that particular instrument. Also, there's always the chance of a toggle switch handle getting snapped off on portable gear. Most of all, those tone stack switches are used only to short out passive components, so they never carry audio that doesn't have an additional path, therefore there's never any switching noise. Even if they failed completely (e.g. after many decades of typical use) the circuits they're in would still continue to operate, so the amp would still be in business. As a fellow engineer, I think you'd appreciate the many details and ideas under the hood in the Solitaire. We'd be honored to build one for you to your specs.

Thanks very much for getting it. There is some excellent DSP coding going down these days, and it certainly has its place. There's just something about tubes that provides an deeply enjoyable experience, so as engineer/musicians we're determined to make tube amps that are as practical as possible to keep that magical flame alive.

Thanks very much for your positive comment. We love to design and build amps that will be around for a long time. I'm looking into getting some help with my videos so they can be a little more frequent and a little less old-school.

Good point!

Thanks very much. I wish we had a Blue kicking around here at the moment so we could try that. It could be a very satisfying combination.

The truth is that push-pull can indeed be Class A, as it is in the Solitare. Unfortunately the music gear world is full of misinformation, which can lead to mistaken assumptions, unfounded prejudices, and a lot of needless dwelling on terminology that isn't widely understood. If musicians would focus on making music and trust their musical sense when choosing gear, a lot of the confusion would just go away.

Well said. This piece is a very, very nice looking piece of kit. I missed the info on the transformers. Did you wind your own? Use toroidal? Either way, Congratulations.@@auburnamplifiers1786

@@auburnamplifiers1786 Mathematics and assumptions..... I can see the visual of the external layout and would assume with the limited space that you run all pre-amp tubes. SO needing two tubes for the push pull and then the PI but that would be particular to getting some power up to drive a speaker....as opposed to signal for a Mixing board per se.....though I haven't dissected your piece or viewed a schematic. SO I would lean ALL pre-amp tubes.....maybe Parallel circuitry....maybe cascading....BUT CLASS A in signal pathway on out to ? SO signal level necessary to drive...something down stream and external.....OR ? and how do you get there with the limited space. Its not quite rocket science level with audio and the infancy aspects of Vacuum tube electronics in the advent of electronics historically. But does make for an interesting POWER RAIL

I did like the one Gibson student amplifier from way way back......Basically a straight up circuit simple and a parallel power tube arraignment for Class A....and more or less the Fender Champ ad extra power tube in parallel..........and lets not get in to field coils...@@auburnamplifiers1786

from my end, unfortunately the collection of RCA books wasn't preserved as family heirlooms....so I gather similar artifacts for the library here and hahaha SAMS. I'm in process of meeting up with an old family associate from the past....that bridges a gap in memory as to being an RCA dealer and then the distribution network and support.....going back to Sarnoff...as there is a BIG Jewish Connection in that pathway if it were Blood once removed or twice removed in that pathway. SO an interesting conversation is coming my way soon. I can recall as a child...visiting NBC in NYC....and my Dad going to the World's Fair prior to WW2.....and The Jewish Family Associate manufacturing RADIO locally in the infancy of Electronics....I recently discovered on the Net here. SO I await where that conversation will go when I meet the old family friend hahaha and the twists and turns & GAPS....and which way does it go@@auburnamplifiers1786

Thank you very much for your kind words and encouragement. All the best to you as well!

Thanks very much. I'm happy to say that Auburn Amplifiers has now reissued this amp in limited quantities, fully assembled by hand. It's at Auburnamps dot com.

Your comment is appreciated - you're only being a 'wise guy' in the most positive sense. Your observations are correct, although those effects will be relatively minor in a guitar amplifier when just tweaking the secondary load to observe the overall effects (output power, distortion characteristics).

@@auburnamplifiers1786 Howdy again. Thank You very much. I observe Hammond guitar output trafos roll off at about 70 - 80 Hz on spec power. So Yes. Minor effect. Regards again.