Thanks for posting the pix of one of my old amps. That one had very good bottom-end response, and followed the musical groove with alacrity, although further improvements have been made to date. It exhibited an extended high-end response that was down about 1.5 to 2.0 db at 40KHZ, depending on the output tube chosen. Rolloff STARTED at about 15KHZ, but was down very little at that point, with a Single-Plate 2A3.. Perhaps some comments on the Buddy Amp that you post can be of some help to forum members: Here goes-- I hope I don't leave anything out!: See that long black A.C. wiring going into the rectifier filament transformer? Why not locate the transformer between the A.C. and the tube sockets, greatly shortening the Line Power leads. This keeps crap from the line out of the aluminum chassis. Two rectifier tubes in parallel? No. Use ONE. You can't use a 5R4. The filament has too small a surface area, and can't deliver enough instantaneous pulse current on top of the idling current.. Use a MODERN 5U4GB. (Example: JJ 5U4GB, or Electro-harmonix 5U4GB. I can only guess, but it looks like the filter cans are probably 70uf or so. C1 and C2. Choke- input is nice here, but those caps should be about 35uf. Oils are OK here. See that big Oil Can as C3? Better get THAT out of there or your Highs are GONE! Looks like you have a nice Plate Choke on the driver tube-- watch its value carefully. Make tests. What is that red cap? Perhaps 4uf Dynamicap? Excellent! Needs a few more small bypassers to extend H.F., or you'll lose some highs here.... Driver plate resistor. Get one that can pass high-energy pulses accurately. I suggest the best 2-watter that money can buy. I don't see any form of voltage regulation on the driver plate supply-- can't tell exactly from the picture, but it looks like only a voltage-dropping resistor. This CANNOT work with a high plate-resistance tube with high gain and low plate current.. The power supply there must be stiff, and have lots of current available. A series voltage dropper resistor KILLS the driver stage thru voltage sag, and current starvation. You won't get enough power to properly drive the 2A3 grid. The amp will be a "wimp"-- both power-wise, and bandwidth-wise. Driver cathode bypass: Get that Solen out of there and get something good-- another Dynamicap with extensive, careful bypassing, or use an Audionote copper foil, etc. Don't do it and kiss your highs and musical swagger goodbye.... That ground on the cathode bypass is crap-- all that other junk on that ground rail before it gets to the driver tube, which is the most important part in the amp! Re-locate the whole layout/grounding scheme. See the driver tube filament leads? Those run right parallel to The cathode SIGNAL leads from the 2A3 filament into the filament transformer. THIS layout has DESTROYED H.F. response in the amp! Re-Do the whole layout! 2A3 cathode bypassing: Get that SOLEN OUT OF THERE! Cheapo! Another place for a bypassed Dynmicap. Or kiss some more highs goodbye... 2A3 cathode resistor: This is a high-current pulsed application, so use either two exactly the same resistors (Mills, etc.) in parallel or use one 50 watt heat-sinked inductive wirewound power resistor. Smaller sizes WILL result in reduced dynamics and bandwidth. See the 2A3 filament transformer mounted right next to the filament transformer for the driver tube? The 2A3 filament trans contains the cathode signal on the 2A3. DO NOT mount ANYTHING near the 2A3 filament trans. Re-do the layout. See how close that 120VAC pilot light is to those two transformers? What do you think the 120V is doing to that whole area? Re-do the layout! Put all 120VAC into one end of the chassis, isolated from all else. Grounding system as a whole: It can't be a series string. It needs to spread-out in increments from a center point, that is bolted to the chassis at a strategic location only. Re-do the layout, starting at the A.C. line ground connection point. 2A3 and driver tube sockets: These will sound better when they have some physical means of isolation from the chassis. Aluminum chassis: This metal will sink high frequencies into attenuation, but will also add a "whitish" (old audiophile term) coloration to all music. This is probably a result of aluminum reacting against the steel in transformers and chokes. For this reason, wood is becoming popular as chassis material. Steel is better-- much better. It is the same thing as the transformers-- that is very good, but transformers have to be elevated above the steel on non-steel mounts. This is to prevent transformer vibrations from shaking the steel chassis, and smearing/reducing high frequencies. Look at my older amp picture. In it, you'll find all of these things, and much more, done right. There is one mistake in my old chassis-- much has been improved since then, but there is one glaring mistake in it: the H.V. output leads from the plate transformer are twisted together. That mistake wasn't made in the Buddy Amp. All of us can still learn... That includes myself. -Dennis-
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