Parts List

Below find a list of some parts you can buy from us to build the Model 91. We do not offer these parts as a complete "kit". Most of you seem to prefer to buy 'ala carte' anyway. That's cool. I've always thought that preparing one's own parts list was an important part of D.I.Y. (means DO IT YOURSELF). We no longer sell some of the small fasteners and other small parts you'll need to finish this project but most of you will be able to find these on your own. This project was designed for those of you who've had some prior experience working on tube amplifiers. If you don't have a good background in practical tube electronics, I suggest that you take a beginning course in basic theory and construction techniques before attempting this project. VOLTAGES FOUND INSIDE TUBE AMPLIFIERS CAN KILL YOU! IF YOU DON'T UNDERSTAND PROPER ELECTRICAL SAFETY PRACTICE, DON'T BUILD THIS AMP! The following list is comprised mostly of parts we used in building the prototype amps shown below. Our criteria included good sound quality, reliability, reasonable cost and good availability from a number of vendors. Feel free to substitute any parts that suit your budget or your peculiar audio/political convictions but I strongly suggest that you stick with the original parts values until you get at least one amp up and running. Sorry, but I decline to comment on or debate the multitude of possible sonic outcomes due to other, more fashionable parts choices, input circuits, etc. The parts described below are for one mono chassis.

1. On-Off switch, metal toggle type, with mounting hardware, see our Connectors pages.
2. AC inlet port, IEC type. See our Connectors pages.
3. Fuse assembly, black phenolic vintage type found on may cool vintage gear, N.O.S. See our Fender Amp Parts pages.
4. 50-100 ohm 2W wirewound pot with locking shaft, N.O.S., various good brands and types. See our Potentiometers pages.
5. Octal tube sockets, Angela ceramic/silver, you'll need two for each mono chassis. If you're building on a tight budget, any of the good octals by QQQ, Omron, Cinch, etc. will work fine. If you've got money to burn, why not use Yamamotos? See our various Angela, Yamamoto and Cinch Octal Tube Socket pages.
6. 300B tube socket, Johnson copy from China is the most popular choice. If you want to use something fancier, try the Angela ceramic silver version or Yamamoto teflon. See our various tube socket pages.
7. Terminal strip, six lug. See our Connectors pages.
8. Terminal strip, four lug. See our Connectors pages.
9. Terminal post. See our Connectors pages.
10. RCA Input Jack, Kimber. See our connectors pages.
11. Oil/Polyprop. 15uF/600VDC, 1.75". See our Angela Polyp. & Oil Capacitors pages.
13. Oil/Polyprop. 30uF/600VDC, 1.75". See our Angela Polyp. & Oil Capacitors pages.
14. Oil/Polyprop. 50uF/515VDC, 2.50". See our Angela Polyp. & Oil Capacitors pages.
15. Clamp, 1.75". See our Angela Polyp. & Oil Capacitors pages.
16. Clamp, 2.50". See our Angela Polyprop. & Oil Capacitors pages.
17. Angela/Jensen .22/630VDC Paper In Oil Copper Foil coupling capacitor with silver leads. See our Angela Paper In Oil Capacitors pages.
18. ANGELA/SCR FAST CAP 15uF/630VDC. See our Angela, SBE, SCR, Etc. Audio Signal Types.
19. ANGELA/SCR FAST CAP 8.2uF/630VDC. See our Angela, SBE, SCR, Etc. Audio Signal Types pages.
20. ANGELA/SCR FAST CAP 22/630VDC. See our Angela, SBE, SCR, Etc. Audio Signal Types pages.
21. 880 ohm 50W non-inductive cathode resistor, made in USA.You won't find this sharp little gold anodized metal jacketed baby at Radio Shack. Best version we've seen so far. See our Resistors pages.
22. 25K/12W Dale resistor. See our Resistors pages.
23. 220 ohm/25W Dale resistor. See our Resistors paes.
24. 50K/25W Dale resistor. See our Resistors pages.
25. 75K/1W resistor. We don't offer this value. Carbon composition, carbon film or wirewound work fine.
26. 91K/1W resistor. We don't offer this value. Here again, carbon composition, carbon film or wirewound works fine.
27. 1.2K/1W carbon film Riken resistor. See our Resistors pages.
28. 390K/1W Riken. See our Resistors pages.
29. 30K/1W Riken. See our Resistors pages.
30. 221K/1W Riken. See our Resistors pages.
31. Filament transformer, 5V/2A with optional dropping resistor. This part is somewhat redundant if you use the Angela Universal Power Transformer but some folks still prefer to use separate filament iron. See our Hammond Transformers pages.
32. Choke, 10H/125mA. See our Hammond Transformers pages.
33. Power Transformer. See our Angela Universal Power Transformer For Tube Amps pages. Anything with similar specifications will work fine. Also see our Hammond Transformers pages.
34. Output transformer? ANY good single-ended hi-fi output transformer in the 2.5-3.5K (or even a bit higher...) works fine. Believe me, the sound quality difference between the budget choices (Hammond 1627SE, Tango U-808, etc.) and the high priced stuff (Tango, Tamura, etc.) is just not as big as you'd think. That's good news to those of you working with a tight budget, since this is one of the few essential part, along with the output tubes, you probably will never find at a Hamfest or surplus sale. See our Hammond Transformers and Tango, Tamura Etc. pages.
35. The Western Electric 300B is a fine choice if you've got a big budget. The Angela/Valve Art Nickel Anode 300B is the best affordable choice. See our Triode Zombies Corner tube pages.
36. GZ37 Mullard. See our Tubes For Guitar Amps And Hi-Fi pages. See our Tube Gallery Pages for a picture of this tube.
37. 6SJ7WGTA JAN Philips/Sylvania, glass bottle, N.O.S. '80s, the best I've heard in this circuit; beautifully built and very lively sounding, reliable too. See our Tubes For Guitar Amps And Hi-Fi pages. See our Tube Gallery Pages for a picture of this tube.
38. Angela Model 91 chassis, heavy gauge aluminum,with massive end billets, center section is finished in black textured Polane, punched out for the parts on this list. See our Hammond, N.O.S., Etc. Chassis pages. For a picture of this chassis, see our J.E. Labs 300B amp project. You can also build the Model 91 project around an inexpensive Hammond 10"X17"X3" aluminum box with cover plate. Here again, see our Hammond, N.O.S., Etc., Chassis pages.

Hints For Builders

1. Upon completion check all solder connections. Most D.I.Y. project problems are due to wiring errors, not 'bad parts', except for maybe tubes and you can eliminate this possibility by simple substitution. The first time you 'fire up' the amp, let it cook for fifteen minutes or so. Anything really stupid you did should show up quickly.

2. Generally we recommend glass 6SJ7WGT types over the easier to find metal versions of this tube type, although the RCA metal 'red tube' 5693 is another good choice. Due to the popularity of this project in the past few years there was a bit of a 'run up' of 6SJ7WGT prices. We fixed that: we bought SIX THOUSAND of 'em

3. Choice of 300Bs? See our Triode Zombies Corner for our current offerings. Avoid Russian 300Bs, also any "VAIC" branded tubes or their relatives, since some dealers are knowingly offering defective/reject tubes for sale.

4. For longest 300B life, make sure that the filament voltage is as close to 5V as possible! If not, you should use a 100 ohm/10W voltage dropping resistor on the filament supply. Connect this dropping resistor in series with the PRIMARY of your filament transformer. Why? Many filament transformers are designed for 115V, so if your line voltage is 120V or over you're going to get a higher than needed filament voltage on the output side.

5. We included a hum balance pot for a good reason. After making voltage checks and hooking the amp into your system, allow ten minutes for warm up, then adjust the pot for lowest hum level, ONE AMP AT A TIME! Believe me, you'll find a point in the rotation of the pot where this becomes obvious. With AC filaments on your power tubes, as found in this project, and especially with single ended, some residual noise will always be present. Don't drive yourself nuts worrying about it! This is usually not a great problem even with super efficient horn systems, although the noise floor will vary according to luck, mostly, we've found. Yes, even N.O.S. $1000 W.E. gems can hum a bit, while Econ-O-Mojo $69 China 300B's will be just as quiet. Yes, the noise floor seems to be unrelated to price or sound quality.

6. Be sure to twist together all pairs of AC carrying wires, including 6SJ7 6V filaments, 120V transformer primary wires, 5V transformer rectifier leads, both primary and secondary leads on the little 5V filament transformer. Why? For the same reason discovered by radio builders in the '20s: to cancel AC hum!

7. I know that this next tip sounds pretty dumb but BE SURE THAT YOU PLUG IN THE 300B TUBES THE RIGHT WAY AROUND! Although I have never even considered doing this, I have, uh, "friends" who've made this mistake so be mindful each and every time you plug in a 300B. REMEMBER! THE TWO BIG PINS ARE THE FILAMENTS AND THE OTHER TWO PINS ARE THE GRID AND THE PLATE!

8. If you're using the Angela Universal Power Transformer, use the two SOLID BLUE wires for the 5VAC filaments of the 300B. You can just put a wire nut on the BLUE/WHITE wire. The BLUE/WHITE wire is a center tap for this winding, allowing the use of 2A3s, etc. in other projects you may build in the future, right? In my opinion, there is no advantage to be gained by using a separate filament supply transformer. We used a separate filament transformer in the early version of this project, as shown in our photos and pictorial, because we didn't have the improved version of the Angela Universal Power Transformer at that time. In the pictorial of the Angela Model 91 we used a transformer with a RED/BLACK wire. Our current Angela Universal Power Transformer has a PURPLE wire with the same function. This PURPLE wire, a 55VAC bias tap, is not needed in this project. This 55VAC bias tap wire is very useful in Dynaco/Marantz/Acrto type circuits. Just put a wire nut on the PURPLE wire if you're building the Model 91. Incidently, the reason we have a PURPLE wire was that our transformer maker did not have RED/BLACK striped wire in his inventory at the time. The two ORANGE wires are additional high voltage taps, more appropriate for the plates of 2A3s and other lower power triodes. Just put a wire not on each of these ORANGE wires if you're building the Model 91. If you've never hooked up a power transformer before, my advice is to pay a local guitar amp repair guy to double check your work before you 'fire it up' for the first time.

9. Wiring up the Angela Universal Power transformer is a job for experienced D.I.Y.ers with a firm grasp of electrical safety procedures and practices. Don't even consider doing this if you've never worked with similar power transformers before! The voltages found in most tube amplifiers can KILL YOU if you don't know what you're doing. For 120V operation, twist together, tightly hand-over-hand, the solid BROWN and solid BLACK leads into a neat pair, guide them toward one lug of the on-off switch, cut to a safe workable length, strip the ends bare just enough, twist the stripped bare ends together tightly, feed these through a single lug hole on the top of the on-off switch and solder securely. Next twist together the striped BROWN/WHITE and striped BLACK/WHITE leads into a neat pair, guide them toward the top solder lug of the fuse holder, cut to a safe workable length, strip the ends bare just enough to twist the stripped bare ends together tightly, feed these through the top lug hole on the fuse holder and solder securely. This completes the wiring of the primary side of the transformer. The pictorial on this site shows the AC connections for a separate 5V filament transformer but that will not be needed if you're using the Angela Universal Power transformer. Next we'll hook-up up the secondary wires of the Angela Universal Power Transformer, starting with the rectifier tube socket. Twist together the pair of solid YELLOW 5V wires into a neat pair and guide these toward lugs #8 and #2 of the rectifier tube socket, cut the wire pair to a workable length, strip the ends bare, insert one YELLOW wire bare end into the top solder lug #8 and solder securely, insert the other YELLOW wire bare end into the top solder lug #2 and solder securely as well. Now twist the two solid RED high voltage (each 380VAC) wires into a neat pair and guide these toward lugs #4 and #6 of the rectifier tube socket, cut the wire pair to a workable length, strip the ends bare, insert one RED wire bare end into the top solder lug #4 and solder securely, insert the other RED wire bare end of the pair into the top solder lug #8 and solder securely. This completes the wiring of the rectifier tube socket for the moment; see the pictorial for connections to the rest of the circuit. Next, twist together the two solid blue 5V wires into a neat pair and guide them toward the 300B tube socket, cut this twisted pair to a workable length, strip the ends bare, insert one BLUE stripped end into one of the 300B filament solder lugs ( one of the two that connect to the BIG holes in the socket body) and solder securely, then insert the other BLUE wire stripped end into the other of the two 300B tube socket filament lugs and solder securely. By the way, W.E. designated pins #1 & #4 as the filament connections but most UX-4 sockets have no number markings so you've got to be careful to make the proper connections. Please consult a 300B data sheet so you understand the tube elements and the associated socket connections. This completes the filament wiring of the tube socket as far as the transformer wires are concerned but you will note that an additional twisted pair of blue wires is also soldered to each the two 300B filament pins and this twisted pair is guided to the two outer lugs of the HUM BALANCE POT where each bare stripped end of this other BLUE twisted pair is also soldered, one BLUE wire to each of the two outer solder lugs. Next, twist the two solid GREEN 6.3V filament wires into a neat pair and guide them toward the 6SJ7 socket, cut this twisted pair to a workable length, strip the ends bare, insert one solid GREEN wire bare end into solder lug #2 and solder securely, then insert the other solid GREEN wire bare end into solder lug #7 and solder securely, completing the wiring of the 6SJ7 filament. Finally, the striped RED/YELLOW high voltage center tap wire of the power transformer and the striped GREEN/WHITE filament center tap are soldered to the ground string at one lug of the 30uF filter capacitor; refer to the pictorial for this step because it will be easier to make all of the connections here at once. As a last step, put wire nuts on all unused wire ends (see step #8 above). If you're not 100% confident of making all of these connections right the first time, try a trial run with the transformer out of the circuit. Try hooking up the primary first, applying AC voltage through a fused Variac, then measure each pair of wires with your meter, making sure that the voltages are in the ballpark (they'll measure somewhat different under load, you'll find). When doing this sort of transformer evaluation, be sure to cap off all wire ends you're not directly measuring with wire nuts for safety. Some reading about power supply design and dual rectification in the RCA Tube Manual is recommended if you'd like to learn more about the 'why' and 'how' of this circuit.

10. Finish the wiring of the rectifier tube socket by cutting an approx. 8" length of YELLOW wire, stripping one end bare, inserting this into the lower hole on lug #8 of the rectifier tube socket and soldering securely. If you're using the Angela Universal Power Transformer, omit the 220 ohm dropping resistor and its associated connections as shown in the pictorial. This wire is then soldered directly to the positive, non-grounded end of the 15uF filter capacitor. Note that if you are using the Angela Universal Power Transformer, the BLACK wire from the Hammond 10H choke and one end of the 50K 25W Dale resistor also connect to this positive, non-grounded end of the 15uF filter capacitor.

11. Now we'll hook up the 10H 125mA Hammond choke. Here's the procedure if you're using the Angela Universal Power Transformer. Neatly twist the BLACK and WHITE wires from the choke neatly together into a twisted pair, and guide them toward the 15uF and 50uF filter capacitors. Solder the bare stripped end of the WHITE wire from the 10H choke to the positive, non-grounded lug of the 50uF filter capacitor. Note that some other circuit elements connect to this lug of the 50uF filter capacitor; one wire from the output transformer primary (see pictorial), a wire leading to the input circuit terminal strip that joins with one end of the 75K 1W resistor and one end of the 25K 12W Dale resistor. Solder the bare striped end of the BLACK wire from the 10H choke directly to the positive, non-grounded end of the 15uF filter capacitor. If you're using the Angela Universal Power Transformer, omit the 220 ohm dropping resistor and connections shown there in the pictorial, instead using the direct connections described in this step. More mind-numbing, terribly redundant and overly wordy 'step by step' instructions will follow as time permits...

Reference Voltages

RANGE	WHERE TO MEASURE	TUBE	FUNCTION
6-6.7VAC	across pins #2 and #7	6SJ7	Filament
5VAC*	across two LARGE pins	300B	Filament
5VAC	across pins #2 and #8	GZ37	Filament
70VDC*	from ground to 300B filament	300B	Bias-300B
110VDC	from ground to pin #6	6SJ7	Screen Supply
3VDC	from ground to pin #5	6SJ7	Bias 6SJ7
425VDC*	ground to 300B plate (red wire)	300B	Plate Voltage
275VDC	junction 25K/30uF cap to ground	6SJ7	Plate Voltage

*Critical Voltage