With very simple circuits like this, the quality of all the active and passive parts is critical. Indifferent capacitors, resistors, and even switches, wire, solder, will be audible. On the other hand, the original idea of this amp was a simple and economical build-up using readily available parts; from orphan old-time gear, where possible. I relate my own experience in implementing and modifying this amp. I'll work from the input to the output. I'll also heat up my good sources the first time I mention them; and once again at the end.

Input Jacks   RCA, 1 pair per input, chassis mount. Should be lightly made of copper, gold plated. Radio Shack sells surprisingly nice ones for little money, part #274-852.

Selector Switch   2-pole, with as many positions as you have inputs, plus one (for a mute position). Should have gold or silver contacts. I only have two sources (tuner and CD), so I use a nice Augat toggle switch that has a center-off position, since a high-quality toggle is far cheaper than an equivalent rotary. Good switches can be had from Michael Percy, and also the bulk vendors (Allied, etc.), if you know what you're looking for.

Volume Pot   100Kohm, stereo (2-deck). Several places have nice ones. Michael Percy and Angela Instruments have the Alps black beauty for $30 or so. The best cheap one I know of is the Radio Shack part #271-1732, made by Alps. Transparent and compact, but not in a can; so, if you mount it to a nonconductive chassis (like I did), you need to use a washer with a wire to ground on the bushing when you mount, or it'll sing when you touch it. RatShack also has a pretty nice 1" aluminum knob for it.

5965 Input / Driver Tube   These are pretty common, and also the similar type 6414. I do not consider the parent type 12AV7 acceptable, although they'll work electrically. Angela has 5965's at an economical price; about $4. I got 30 of 'em a few years ago when they were unknown and Steve was selling them for 67 cents. Eat your heart out. This is a dual triode; the two devices shown are actually one tube.

60K and 63K 2W Plate Load Resistors   This is a critical part. I've tried garden-variety metal films here, and the sound suffered. The amp shown has two 30K 1W Holco's in series on one side, and a Holco and a 33K 1W Riken on the other. These are the old non-inductive Holco's which are no longer being made, and I think the Riken sounds better anyway. The problem is that the Riken's don't come in close enough values to get the composite value needed. A nice looking similar resistor is the Kiwame, which Michael Percy has. Angela has the Riken's. These resistor composites are dissipating about half a watt each, so they're just over the limit for a 1-watt part; but using series or parallel combinations of two 1-watt parts you can use substantially different values without problem.

25.5K 4W 'Longtail' Driver Cathode Resistor   This is maybe the least critical part in the circuit. Actually 56K and 47K 2W metal oxide power resistors in parallel; I tried better resistors and could hear no difference whatever. I got an assortment package of metal oxides from Mouser that has about a bushel of 'em for, I think, thirty bucks; for experimenting. You can use Kiwame 5-watters from Michael Percy at 2 dollars; even better.

.33µF Coupling Capacitors   These are another critical part. I use 400V Jensen paper-in-oils, which are very good. They ought to be; they cost nearly twenty bucks each, and are about the size of a 'C' battery. Michael Percy has 400V Auricaps, which many people like better, for $5.50.

.01µF Bias Noise Shunt Capacitor   This is a good implementation trick for high impedence power supplies of all kinds, which most vacuum tube supplies are. The bias adjust pots that are shown in the power supply schematic are actually located right between the output tubes, with the bias test point (which is in the output tube cathode circuit) right next to it. You can see this in the the photo of the amp. The 34Vdc from the bias supply connects to the 'down' (counterclockwise, from the shaft side) end of the pot, and the 'up' end of the pot to ground through the 4.7K 1/2W resistor. The wiper of the pot accepts the two 100K resistors that go to the output grids, and this little cap; which shunts any noise / hum that this high impedence circuit might pick up to ground. Gives a nice, quiet bias supply. This should be a film-foil type, for high current-slope capability, and Angela sells the Sprague 716P for under a dollar. Get plenty, in .01, .1, and .25µF values; they're used all over this circuit, you'll see.

100K and 100ohm Bias Circuit and Screen Coupling Resistors   Regular 1/2 watt metal films work fine here, and are what's in my amp; although if you're ordering from Angela, Riken 1/2 watters would be superior. Those cheesy 1/2 watt carbon films that RatShack sells are amazingly good if there's no current in them; but at a signal level approaching 16vac, I think they'll get crunchy and noisy. If you're over at Mouser, Dale (Vishay) metal films look good. I suspect these of being successors to the Dale 'hot dogs' I used to get from Unca Ned at Triode Electronics, which were quiet and clear.

6V6 Output Tubes   These are available all over the place in NOS versions at (usually) reasonable prices. I've never heard a bad 6V6, one of the reasons I chose this device; but I've heard that most of the current-production Russian types are pretty raggedy. A possible exception is the new ElectroHarmonix, from Sovtek. Triode Electronics has these, and so does Antique Electronic Supply, very reasonably priced. The ones I mostly use are GE wafer-base JAN types from Angela which sound as good as any I've tried (a bit fizzy when they're new), are cheap and plentiful, and nice looking. Don't laugh; a lot of 6V6's are painted black inside, including the fabulous NOS RCA's. As a detour, this circuit is quite suitable for the very similar (electrically) 6BQ5 / EL84 type, which I have heard is also a very good sounding device, and even more available than the 6V6. The only modification to the circuit would be to drop the primary B+ voltage from 315v to 300v, which is the screen max for the EL84.

Output Transformer   7.2K to 10K primary impedence. The output tranny is the biggest, most expensive, and arguably most critical component in the circuit. A primary impulse for the development of this amp was, in fact, the recycling of output and power transformers from 6V6 and EL84 consumer hi-fi amps and receivers from the late tube days. There are still quite a few of these in attics and garages, and the 'dead' shelves of audio fix-it places. The transformers in these pieces are of surprisingly good quality, and the gear is generally non-operative, so it can be gotten very cheaply; often free. The outputs in my amp are from a Harmon Kardon HK-240 receiver. All that's neccessary is to determine that the original piece used 6V6's or EL84's in the output, and the transformer will be of the correct primary impedence; usually 7.2K. If the tubes themselves aren't in the sockets, the type is usually printed next to the socket on the chassis. If you can't tell, get it; what's five bucks? You're stocking yourself up for future projects. I never refuse the offer of an old tube piece, even the dreaded Dyna 70. I'll go into the salvaging of trannies in another section, but it's pretty commonsense, and mostly just involves carefully observing where all the leads go to in the original circuit, then testing for voltage. There are also a good number of output transformers being currently made specificaly for PP EL84's and 6V6's. Magnequest makes a nice 7.2K, which Triode Electronics carries; it's a drop-in upgrade for the Dyna ST/SCA-35. Mikey is the most highly respected winder in the US, and this trans is quite economical. The cheapest is the Hammond, in both 8K and 10K, which Angela has. Audio Note Great Britain also has an 8K type, the TRANS-200, and I've had very good results with other models of theirs. Also in Blighty, Brian Sowter makes good ones, the U064 8K, and U067 9K. Look on these guys' sites for US distributors.

Sockets, Wire, Solder, Etc.   All this stuff is important. Sockets, I use nice ceramic-gold sockets for the 9-pins, and Cinch mil-spec micanols for the octals; everybody has them, order when you order the rest. Wire, I use regular 18ga solid core from Radio Shack for nonsignal stuff like filaments and unmodulated DC. RatShack Rainbow Wire sliced apart is also good for, like, bias, or wherever a smaller wire is needed. No matter what Cory says, this stuff is no good for signal, but it's nice to work with; the clear outer sheath being quite resistant to melting. A caution: a lot of otherwise good-ish (for audio) quality wire, like non-plenum cat5, has polyethylene or polypropylene insulation. This is low temperature plastic, and is very unhappy inside a warm chassis in the long term. It will discolor and crack and generally not say good things about your product quality to some tech ten years down the road. I use regular PVC wire for nonsignal, and teflon for signal; nowadays mostly the conductors from cat5 plenum, Belden hi-temp when replacing grotey old transformer leads. Long signal runs should be shielded; I use Radio Shack 6mm Mega-Cable (that they sell unterminated in 6ft lengths) with the PVC outer sheath carefully sliced off and replaced with teflon plumber's tape or cloth tubing. The copper braid protects the poly foam dielectric from the heat well enough, and the stuff sounds good. Solder, I've always used the SN62 ('Electronic silver solder') from Radio Shack, but the newer version (with the purple ink on the spool label) is not as nice to work with; although it's okay if you keep the iron real clean. Next time I order from Percy, I'll get a quarter pound of Wonder or Cardas.

The List   Again, here are the guys I use; in no particular order of preference, but frequency of use.

• Angela Instruments   Tubes, sockets, resistors, capacitors, transformers, chokes, other stuff. Nice folks.
• Triode Electronics   Tubes, sockets, transformers, Other stuff. Good links to tube data and schematics.
• Michael Percy   Wire, solder, switches and pots, connectors, capacitors, resistors, the fancier stuff.
• Antique Electronic Supply   Tubes, sockets, interesting transformers, capacitors, guitar amp and old radio parts.

• Mouser Electronics   Dale resistors, switches, cat5plenum wire, UF diodes. A smaller general vendor.
• Digi-Key   Much like Mouser, some different brands.
• Allied Electronics   The biggest of the general vendors. Higher voltage transformers, chokes, lots of groceries.
• Audio Note Great Britain   Nice transformers, also tube kits and other parts.
• Sowter Transformers   Very good transformers. Specializes in custom winding, if you get that far.

There’s always the impulse, when we come upon a really good sounding circuit like this, to build one all out of boutique parts; but that really wasn’t the idea of this amp, and it still isn’t. This circuit builds up easily using a lot of orphan late-model consumer parts, along with selected decent modern components, and will allow a Boy and his Soldering Iron to cheaply find out just how much six watts amounts to; as well as how much natural resolution these simple no-feedback triode amps are capable of. As much as I aspire to be an internationally notorious genius, I get the sinking feeling that there’s really nothing that special about this circuit: I have the awful suspicion that back in the 30’s, when most gear was quite similar to this amp, there was a lot of good sound floating around.

That's all I can think of. If I've left anything out, or you have other questions, give me a hoot at poinxie@yahoo.com. I'm working on making this amp buildable from the page, and I welcome suggestions.

Poinz