diytube stereo 35 Installation instructions

diytube
stereo 35 power amplifier
rev c
INSTRUCTIONS FOR
ASSEMBLY
OPERATION
Price $10.00

Disclaimer
DisclaimerDisclaimer
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
Warranty InformationWarranty Information
Warranty Information
All goods purchased from diytube have a thirty (30) day warranty from
the date of purchase against defects.

Istrongly suggest you completely read this manual before
Istrongly suggest you completely read this manual beforeIstrongly suggest you completely read this manual before
Istrongly suggest you completely read this manual before
you turn on your iron or get out the cutting oil.
you turn on your iron or get out the cutting oil.you turn on your iron or get out the cutting oil.
you turn on your iron or get out the cutting oil.
Preparation
PreparationPreparation
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
note that the vacuumnote that the vacuum
note that the vacuum
tube sockets can only be mount
tube sockets can only be mounttube sockets can only be mount
tube sockets can only be mounted on the non
ed on the noned on the non
ed on the non-
---silkscreened side. silkscreened side.silkscreened side.
silkscreened side.
Overview of the Schematic and Design
Overview of the Schematic and DesignOverview of the Schematic and Design
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 330-490
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
Using the Assembly DrawingUsing the Assembly Drawing
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
SolderingSoldering
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. When soldering these components, let the solder flow through
the hole to form a ‘teepee’ on both sides of the board for an optimum
connection. Ground plane connections sink a lot of heat from the
soldering iron, so take care to do these well- you may have to touch up
from the opposite side.

TIP: PCB Stuffing
TIP: PCB StuffingTIP: PCB Stuffing
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.
1. Stuff all fixed value resistors into the PCB. Mount R36 and R34 on the
opposite side of the PCB (ie 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 (non-silkscreened) 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
to the non-silkscreened side. 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. Stuff R42, the IRCL, making sure it doesn’t lean on or touch the J1
terminal block as it gets warm.
10. Stuff the 4 filter capacitors. Mind the polarity. If these are
substituted, the diameter must be 25mm or less. The height must be
30mm or less to fit in a 2” high chassis.
11. Carefully go over your work, looking for:
a. any cold solder joints (these will look dull)

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
Initial Impedances: When it DoubtInitial Impedances: When it Doubt
Initial Impedances: When it Doubt, Ohm it Out
,Ohm it Out,Ohm it Out
,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. GND
6. GND
7. 100 [50]
8. 100 [50]
9. >10M
10. >10M
J2
1. >10M
2. >10M
3. GND
J3
1. >10M
2. >10M
3. 28.3K [1 ohm]
J4
1. >10M
2. >10M
3. 28.3K [1 ohm]
J5
1. >10M
2. >10M
3. GND
J6
1. >10M
2. GND
J7
1. >10M
2. GND

Initial Settings: Feedback and Bias
Initial Settings: Feedback and BiasInitial Settings: Feedback and Bias
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.
1. To set the negative feedback when using the variable resistors (R30
&R31), unhook any connection to J3-3 and J4-3 and measure from
those points to ground with a DMM. Your exact value is 1.3k less
(due to the cathode resistors on V1). Set to 28.3k if using a 16 ohm
tap as the feedback tap, or 20.3k if using an 8 ohm tap.
2. Adjust the bias pots (R19,R22,R25,R28)until you measure around
400 ohms from pin 3 of V3,V4,V5 and V6 to ground.
Ad
AdAd
Adjusting Bias
justing Biasjusting Bias
justing Bias
WARNING: This is done while the unit is ON and IDLE. Take care
and follow proper high voltage safety rules.
With an insulated adjustment tool and a DMM (at low voltage setting),
adjust bias pots clockwise (up) or counter-clockwise (down) to get the
voltage at each TP (i.e. the test point at R19,R22,R25,R28) to be 350mV.
This means the cathode current is 35mA. Plate current is about 30mA
and the screen is 5mA. Bias all four tubes this way. Check again after a
few hours use and readjust if necessary. Check again after one week,
then one month.
Voltages
VoltagesVoltages
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
1116 207 - - - -
2 0 116 0 0 0 0
3780mV 120 13 13 13 13
43.1VAC 3.1VAC 3.1VAC 3.1VAC 3.1VAC 3.1VAC
53.1VAC 3.1VAC 3.1VAC 3.1VAC 3.1VAC 3.1VAC
6115 208 - - - -
7 0 114 360 360 360 360
8780mV 118 - - - -
93.1VAC 3.1VAC 364 364 364 364

Modifications
ModificationsModifications
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 &
3will be nearly the full range of the pot. If using a stereo pot,
follow the same process with pins 4, 5 & 6.
•A100 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
2on 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.

diytube Stereo 35 Rev C Revised: Sept 3, 2010
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.
Item QTY Reference Part Mouser Part Unit Cost
_________________________________________________________________________
2 R1,R2 47.5k, 1/2W 71-RN65D-F-47.5K 0.31
6 R3,R4,R13,R14, 475k, 1/4W 71-RN60D-F-475K 0.23
R15,R16
2 R5,R6 1.27k, 1/2W 71-RN65D-F-1.27K 0.31
2 R7,R8 301k, 1/2W 71-RN65D-F-301K 0.31
2 R9,R10 27k, 1W 281-27K-RC 0.13
2 R11,R12 33k, 1W 281-33K-RC 0.13
4 R17,R20,R23,R26 470, 3W 72-RWM410-470-5 0.57
4 R18,R21,R24,R27 1k, 1/2W 71-RN65D-F-1.0K 0.31
4 R19,R22,R25,R28 10K Pot 72-T93YB-10K 1.44
1 R29 300k, 1W 594-5083NW330K0J 0.32
2 R30,R31 100K Pot 72-T93YB-100K 1.44
2 R32,R33 3.3k, 3W 72-RWM410-3K3-5 0.75
4 R34,R35,R40,R41 100, 3W 72-RWM410-100-5 0.57
2 R36,R37 Jumper Use cut leads 0.00
2 R38,R39 150k, 1/2W 71-RN65D-F-150K 0.31
1 R42 Inrush Limiter 527-CL90 1.72
4 R43,R44,R45,R46 10 Ohm, 1/4W 71-RN60D-F-10 0.12
4 C1,C2,C3,C4 0.1uF,400V 75-715P400V0.1 1.38
4 C5,C6,C7,C8 470uF,35V 647-UVR1V471MPD 0.48
4 C9,C10,C11,C12 120uF 5985-380-450V121 3.57
2 C14,C15 Jumper Use cut leads 0.00
2 C16,C17 27pF 5982-15-500V27 1.13
2 C18,C19 33pF 5982-15-500V33 1.13
2 C20,C21 15pF 5982-15-500V15 0.72
2 C22,C23 0.22uF 5989-250V.22-F 0.65
2 D1,D2 UF4007 Diode 625-UF4007-E3 0.19
1 J1 10pin .375” Block 571-114376644 4.89
4 J2,J3,J4,J5 3pin .375” Block 571-14376645 1.08
2 J6,J7 2pin .375” Block 571-14376644 0.54

diytube Stereo 35 Rev C Revised: Sept 3, 2010
Item QTY 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.
1 SW1 Power Switch 103-R13-112B-02G-EV 1.29
1 SW2 Standby Switch 103-R13-112A-02-EV 0.99
1 F1 Fuse Holder 504-HTB-26M 2.13
1 F1 2A Midget Fuse 504-GMA-2 0.26
1 3-Prong AC cord 173-53101-E 2.80
1 Strain Relief 561-MP5N4 0.10
1 Stereo Volume Pot 313-2420-100K 2.35
Note: Hammond product is very inexpensive at www.angela.com
1 12X8X2 Chassis 546-1444-22 20.22
1 12X8 Bottom 546-1434-22 8.66
or
1 12X10X2 Chassis 546-1444-29 20.35
1 12X10 Bottom 546-1434-29 8.66
Note: These aren’t $30, gold-plated interconnects. Due to the small quantities of nuts & bolts, you
might want to buy these at your local hardware store. The Mouser parts are nickel plated and in
boxes of 100. Don’t forget solder, spade connectors, etc.
1 RCA Red Jack 161-0251-EX 0.87
1 RCA Black Jack 161-0252-EX 0.87
4 Binding Posts 164-4205 1.29
2 Binding Posts 164-4201 1.29
2 Red Test Points 151-307-RC 0.28
2 White Test Points 151-301-RC 0.28
8 Standoffs 1/4X1/2 534-1451C 0.45
6 Bushings 534-744 0.49
1 box (need 16) 6-32x1/4 screws 5721-632-1/4 1.77
1 box (need 8) #6 lock washers 5721-LWI-6 1.57
1 box (need 12) 10-32x3/8 screws 5721-1032-3/8 2.95
1 box (need 12) #10 flat washers 538-MW-404C 2.00
1 box (need 12) #10 lock washers 5721-LWI-10 1.82
1 box (need 12) 10-32 hex nuts 5721-1032 2.56

diytube Stereo 35 Rev C Revised: Sept 3, 2010
Item QTY 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.
1 V1 12AX7A/ECC83
1 V2 12AU7A
4 V3,V4,V5,V6 6BQ5/EL84/7189/6p14p
6 V1-V6 9pin PCB Ceramic Socket
1 T1 Dynaco PA-774 Power Transformer
or
1 T1 Hammond 270HX Power Transformer
2 T2,T3 Dynaco Z-565 Output Transformer
or
2 T2,T3 Hammond 1650F Output Transformer
Note: Hammond 1650E (8k) and 1620 (6.6k) have been used as well.
Triode Electronics -- aka Uncle Ned http://www.triodeelectronics.com/
Angela Instruments -- http://www.angela.com/
Antique Electronics -- http://www.tubesandmore.com/
Handmade Electronics -- http://www.hndme.com/
Prices Not Current!
Triode Electronics Angela Instruments Antique Electronics Handmade Electronics
Dyanclone PA774 $65.95 Hammond 270HX $45.00 Hammond 270HX $62.38 Hammond 270HX $69.31
Dynaclone Z565 $78.00 Hammond 1650F $47.00 Hammond 1650F $55.22 Hammond 1650F $61.36
9pin Ceramic PC $1.95 Hammond 1441-22 $19.00 9pin Ceramic PC $2.50 9pin Ceramic PC $1.95
Sovtek EL84 quad $23.90 Hammond 1434-22 $7.25 EI EL84 quad $31.80 Hammond 1444-24 $20.45
12AX7 $5.95 12AX7 $6.95 Hammond 1434-22 $8.66
12AU7 $6.95 12AU7 $4.75