I've always wanted to just build a straight 5E3 clone....but don't think I could keep myself limited to the task long enough, and to not elaborate on the original design. Then again, maybe a Harvard would be better. So, I have everything I need lying around for a tweedy styled 6V6 amp. Power transformer from a 1960 Clavioline, Ca. 350V HT, 5Y3 rectifier, plenty of filament ampere. Output transformer from my Super Champ with 8K5 plate load from 8 Ohm.....maybe an 8K or even a 6K6 would be better, but I will use what I have. I think I have all the necessary switches, resistors, caps pots etc. that I will need, as well as a novel cab idea, so lets get on with thinking about the schematic. The Harvard 5F10 & 5E3 Deluxe will definitely stand as model for my new amp, and although I will add several modifications to the 1950's concept. I will limit myself to one input and channel, and use only two knobs; volume and tone........BUT.........I will be making both those pots push/pull switching, to be able to achieve a variety of tonal variation. So what are the differences and the similarities between the 5F10 & 5E3 from an electrical standpoint ? The input stage has the obvious difference of tube. The two halves of the 12AY7 vs. the 6AT6 (similar to half a 5751) This was also alternatively fitted with a 6AV6 (similar to half a 12AX7(ignoring the diode sections)). So, one channel instead of two. The input resistors relate to each other as shown here below. Obviously the Deluxe has no middle input, but both channels have the same arrangement for the top and bottom input. That the Harvard has no ground reference for the grid, other than through whatever is plugged in, is strange. The differing tube stages are followed by a coupling capacitor leading to the identical tone and volume controls. In the 5E3, this is 0.1µ, whereas the 5F10 uses a much smaller 0.02µ cap. The phase inverter stage identical in the two amps, other than that the driving stage of the 5F10 has an unbypassed cathode resistor, necessitated by the fact that this would ground out the negative feedback that is fed in at this point, unlike on the 5E3 which has no NFB coming from the output transformers secondary side. The push-pull 6V6 power amp section of the two amps differs in that the 5E3 is self/cathode biased, whereas the 5F10 has a fixed-bias arrangement, along with the negative supply this necessitates. The 5F10 transformers: O.T. - 125 AIA 6.6K : 8 Ohms P.T. - 125 PIA from Woodward-Schumacher. I could find no additional information regarding this transformer, other than the schematic showing the low voltage of 305V at the O.T. centre-tap (315V on the 6G2). The 125PIB was possibly also used, this would have voltages more like the 360V or so we might expect to find in a 5E3. The 5E3 transformers: O.T. - 8K : 8 Ohm P.T. - 6452-E from Triad 325-0-325V. Then getting to the output, the 5E3 has a 12" speaker and no NFB, whereas the 5F10 used a 10" speaker, and does have NFB. So, similar in some ways....very different in others. Could one bring both these amps together in one amp? Maybe not, but that is not going to stop me being inspired by both, and utilizing aspects from both. Let's therefore call it a "HARVALUXE" The amp will have various modifications that are not unusual to see in modded 5e3's.....plus some others maybe. Opting for a 12AY7 input tube, I have decided to run the two halves parallel, but each slightly differently, in the hope of a more colourful sound. While one half is more mid balanced, the other is somewhat brighter, with the addition of a switchable mid-cut option. (tone pot pull switch) These are fed into a standard tone/volume stack, with a somewhat smaller treble bleed cap than 5E3 specs. The phase inverter driver stage, is taken, like the output transformer and NFB loop, from the Super Champ. Here we have the luxury of a bypass cap boost for the stage, as well as a moderate feedback. The NFB is minimized with the volume pot pull switch. The phase inverter has an added grid resistor, as do the output tubes, in order to suppress unwanted phase-inverter distortion. An adjustable negative voltage supply has been tapped off the H.T., and the option of switching between fixed and self/cathode bias is made possible through the second part of the volume pull switch. This way I get fixed bias with NFB like the Harvard, and self bias without, like the Deluxe. The addition of the small filter-choke after the screen supply, was chosen to allow screen-grid sagging to happen, whilst dropping the preamp tubes voltage as little as possible, but still supplying sufficient filtering. This is because the 12AY7's work best with a higher voltage than the 5E3 normally puts on them. So here is my schematic as it stands at the moment. Any suggestions as to alterations would be of interest. Any finalization of component values will first be possible after getting the thing up and running, as will knowing what the actual running voltages are. Now off to do some metal-work on the chassis, and finding the bits for building the power supply.