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Summary of Contents for diytube stereo 35
- Page 1 35 power amplifier rev d INSTRUCTIONS FOR ASSEMBLY OPERATION Price $10.00...
- Page 2 Disclaimer Under no circumstances does diytube assume liability or responsibility for injury or damages sustained in the assembly, test or operation of this kit or for damages to any other equipment connected to it. As this is a partial kit, proper assembly is buyer’s responsibility. diytube reserves the right to make design changes or improvements without the obligation to revise prior versions. All specifications are subject to change without notice. • WARNING: Lethal voltages (greater than 400VDC) are present in this project. • Use a Variac or isolation transformer while working on and testing the unit. • Use a rubber mat to stand on while working on and testing the unit. • Keep one hand in your back pocket if probing voltages with a DMM. • Wrap a small piece of electrical tape around the test lead probe shaft to expose just the tip. • Do not connect or disconnect wires to the terminal blocks when unit is powered or plugged in. • Lethal voltages exist in the capacitors even after unit is powered down, so wait at least one hour to after unplugging to allow charge to dissipate. Warranty Information All goods purchased from diytube have a thirty (30) day warranty from the date of purchase against defects. ...
- Page 3 I strongly suggest you completely read this manual before you turn on your iron or get out the cutting oil. Preparation Before assembly, some preparation needs to done. Parts must be purchased, a work area needs set up and chassis decisions should be made. The axiom haste makes waste has never been more true. Make sure your chosen transformers and the board will fit comfortably using the chassis of your choice. The PCB itself makes a perfect template, as shown on the website, for socket and mounting holes. Be sure to plan where RCA connectors, binding posts, standby & ON/OFF switches and the AC cord will be oriented on the chassis. Physically lay out the parts in a space equal to your chassis to assure everything fits. Also, note that the vacuum tube sockets can only be mounted on one side, which is designated in the silkscreen. Overview of the Schematic and Design The design closely resembles the Dynaco Stereo 35. The use of one 12DW7 per channel has been replaced by ½ a 12AX7A and ½ a 12AU7. The 12AX7A is a voltage amplifier that directly drives the 12AU7, a cathodyne phase splitter. The only other meaningful change is the replacement of a single cathode resistor and capacitor with four individual resistors and capacitors. A larger value resistor in series with a variable resistor parallels the main cathode resistor, providing a range of 320‐450 ohms per cathode. This circuit is then in series with a 10 ohm resistor to calculate the current very easily via a test point ‐ set conservatively for 350mV, thus 35mA. Using the Assembly Drawing The assembly drawing is a quick reference to what component is where and the numbering scheme for the connectors. It is also a good place to make any notes. Soldering This PCB is a double‐sided, plated through‐hole design on .094” FR4 material with LPI (liquid photo‐imagable) solder mask and 2 ounce copper per side. ...
- Page 4 TIP: PCB Stuffing Use the flat end of the 10‐pole terminal block as a lead bending tool. This works for most of the parts. Do take care to not damage the meniscus of the components. Insert all resistors before soldering, bending the leads down to hold them in place. This allows one to fix any placing errors that might occur very easily. Use a good pair of snips to remove the excess leads. The top side of the PCB is designated as the side with the ground plane and with the sockets marked as ‘THIS SIDE ONLY’. 1. Stuff all fixed value resistors into the PCB. Mount R36 and R34 on the opposite side of the PCB (i.e. opposite of R37 and R35). This is to maximize heat dissipation. 2. Stuff variable resistors. You may choose to put them on the top side of the PCB and drill extra holes in your chassis for external adjustments. There are guides hole in the PCB for this. Also, be sure you will can easily insert a DMM probe between the resistors. 3. Kink leads on the silver mica capacitors and stuff. 4. Stuff D1 and D2. Mind the orientation of the cathode, which is represented by a stripe on both the silkscreen and the diode’s body. 5. Stuff C5,C6,C7 & C8. Mind the polarity. The board has “+” symbols to show where the positive terminal from the capacitor should be placed. Note that many modern caps have only the “‐“ terminal marked, usually with a stripe running down one side. If you choose to substitute, the diameter must be no more than 10mm. Use a smaller value, for example 100uF, if necessary. 6. Stuff all the polyprop capacitors. 7. Place and solder all the tube sockets – make sure they are mounted on the top side only. It is recommended to use an old miniature nine pin tube to break in the sockets. I have found a very small nail works well for me – but don’t break the ceramic! 8. Place and solder the terminal blocks. Do not over solder the connectors as solder could then spill under the connector causing a short. 9.
- Page 5 b. solder splashes and shorts between socket pins c. any connections that solder didn’t flow to the other side (like ground plane connections) d. snip excess leads e. compare your board to photos from the website – a good check for capacitor orientation Initial Impedances: When it Doubt, Ohm it Out These are without connections to the terminal blocks. When connected, those readings that will differ will be in brackets. Different transformers will have different readings – this one is a PA‐774. J1 1. >2M [94] 2. >2M [94] 3. >200K 4. >200K 5.
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Page 6: Adjusting Bias
J6 1. >10M 2. GND J7 1. >10M 2. GND Initial Settings: Feedback and Bias WARNING: Do these adjustments with the unit off and unplugged, as well as having had one hour to bleed voltage from the filter caps. Note: Most amps will just use a fixed resistor here, but the diytube circuit uses a pot for experimentations sake ‐ thus this extra step. 1) Donʹt have your negative feedback connected yet, that is your output secondary or else it will be a real low impedance. 2) Probe your DMM from J4 pin 3 (right channel) to ground and adjust R30 until the resistance is 20.3K (set to 28.3K if using the 16 ohm tap as feedback, as in the original Z565). 3) Probe your DMM from J3 pin 3 (left channel) to ground and adjust R31 until the resistance is 20.3K (set to 28.3K if using the 16 ohm tap as feedback, as in the original Z565). 4) Your feedback is set. Adjusting Bias ... - Page 7 WARNING: The following is done while the unit is ON and IDLE. Take care and follow proper high voltage safety rules. 5) With all your connections in place, power up. Your initial bias has been set ‐ this makes sure that you donʹt accidentally have a tube aggressively biased, and they should all end up near the same range on power up. 6) Probe your DMM (set to DC volts) from the test point which is sandwiched between the R19 & R22 to ground. V3 is adjusted with the ʹinsideʹ test point. Adjust R22 until the voltage is .350V or 350mV. 7) Probe your DMM (set to DC volts) from the test point which is sandwiched between the R19 & R22 to ground. V4 is adjusted with the ʹoutsideʹ test point. Adjust R19 until the voltage is .350V or 350mV. 8 ) Probe your DMM (set to DC volts) from the test point which is sandwiched between the R25 & R28 to ground. V5 is adjusted with the ʹinsideʹ test point. Adjust R28 until the voltage is .350V or 350mV. 9) Probe your DMM (set to DC volts) from the test point which is sandwiched between the R25 & R28 to ground. V6 is adjusted with the ʹoutsideʹ test point. Adjust R25 until the voltage is .350V or 350mV. Voltages These are zero‐signal, nominal measurements in VDC, unless otherwise noted. They are all referenced to ground. PIN V1 V2 V3 V4 V5 V6 1 116 207 ‐ ‐ ‐ ‐ 2 0 ...
- Page 8 Modifications • If volume controls are desired, use a 100k or better audio taper pot. A linear pot will not work correctly. You can salvage the 250k pot off of your Dynaco SCA‐35. Radio Shack has a 100k Alps stereo pot that many people use. Each channel must have its own control, so either a stereo pot or two single pots must be used. The pot connections will be: ‐pin 1 to RCA audio IN ‐pin 2 (the wiper) to J6‐1 or J7‐1 (depending on channel) ‐pin 3 to J6‐2 (GND) or J7‐2 (GND) To determine which pin is which, use a DMM and crank the volume pot fully counter‐clockwise (lowest volume setting). Resistance between pins 1 & 2 will be nearly the full range of the pot. Pins 2 & 3 will be very low resistance. Rotating the pot fully clockwise (highest volume setting) will yield opposite results, i.e. pins 1 & 2 will be very low resistance and pins 2 & 3 will be nearly the full range of the pot. If using a stereo pot, follow the same process with pins 4, 5 & 6. • A 100 ohm 1W resistor (Mouser# 281‐100) can be soldered on the underside of the board between pins 1 & 2 on J2,J3,J4 and J5 for triode operation. Do not attach any UL taps to pin 2 on these connector blocks if you do this. Do not populate C20 & C21. • If you are using a filament supply with a center tap and choose to use the center tap, do not populate R40 and 41. These are for non‐ CT filament supplies, such as the Dynaco PA‐774. • SW2 can be omitted and the secondary CT wired straight to ground if a standby switch is not desired. • R42, the IRCL, is very important for proper operation of this unit. It is possible to wire a switch in parallel with it in order take it out of the circuit once the unit has warmed up, but this is not recommended‐ especially for Hammonds, as they are rated at 115VAC. Note: This will increase the B+ by around 12V and will slightly increase heater voltage. Switch would need to be reset as well. •...
- Page 9 Stereo 35 Rev D Revised: November 30, 2008 Tip: Put a dot in the checkbox if you have the part already as a quick reference when ordering parts. ‘X’ out the checkbox when you have installed the part on the PCB.
- Page 10 Stereo 35 Rev D Revised: November 30, 2008 Item Reference Part Mouser Part Unit Cost _________________________________________________________________________ Note: Change the last letter of the part number, ‘G’, to a ‘Y’ or ‘R’ for a yellow or red neon indicator on the power switch. Default is green.
- Page 11 Stereo 35 Rev D Revised: November 30, 2008 Item Reference Part Mouser Part Unit Cost _________________________________________________________________________ Note: I’m assuming this is the area people will improvise most, and with parts they have on hand. I highly recommend parting out a Dynaco SCA-35 as these are the same transformers found the in the highly regarded Dynaco ST-35.
- Page 12 V3 EL84 J2 Output Transformer Hookup i/c'' i/c''' 0.1uF J7 Left Channel Input 470K PF left 470uF 6.3VAC B 6.3VAC A 150K 470K 33pF 0.22uF 470uF R3 470K 0.1uF R5 1.3K i/c''' NF left i/c'' 15pF V4 EL84 PF left R12 33K 320V NF left...
- Page 13 320V D1 UF4007 100, 3W D2 UF4007 3.3K, 1W 3.3K, 1W 100, 3W CON10 120uF 120uF 120uF 120uF 300K Keystone CL-90 .05, 3W ww 6.3VAC A 6.3VAC B .05, 3W ww...
- Page 14 Z-565 8 OHM green/white Left Output Transformer blue/white black blue yellow 16 OHM green orange Z-565 8 OHM green/white Right Output Transformer blue/white black Right Channel Logical Layout of the diytube Stereo 35 Left Channel with Dynaco Transformers...
- Page 15 8 OHM brn/yel grn/yel Just think green/yellow to green, and black/yellow to black. blk/yel 4 OHM blu/yel green blue black Hammond Style Right Output Transformer Right Channel Logical Layout of the diytube Stereo 35 Left Channel with Hammond Transformers...
- Page 16 320V JUMPER J7 Choke JUMPER 3.3K, 1W 3.3K, 1W CON10 120uF 120uF 120uF 33uF 300K Keystone CL-90 jumper 6.3VAC A 6.3VAC B jumper...
- Page 17 8 OHM brn/yel grn/yel Just think green/yellow to green, and black/yellow to black. blk/yel 4 OHM blu/yel green blue black Hammond Style Right Output Transformer Right Channel Logical Layout of the diytube Stereo 35 Left Channel with Hammond Transformers...
- Page 18 320V JUMPER J7 Choke JUMPER 3.3K, 1W 3.3K, 1W CON10 120uF 120uF 120uF 33uF 300K Keystone CL-90 jumper 6.3VAC A 6.3VAC B jumper...
- Page 20 9.250 1.000 1.260 3.480 0.300 4.625...
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