The Dynaco Tube Audio Forum

Dedicated to the restoration and preservation of all original
Dynaco tube audio equipment - Customer support for Dynaco VTA tube amp kits, all
Tubes4hifi.com products and all Dynakitparts.com products

Home  Calendar  Gallery  FAQ  Search

Search Query

Display results as : Posts
Topics

Advanced
Search

Memberlist  Usergroups  Profile  You have no new messages  Log out [ dmfraser66 ]

View
posts since last visit

View
your posts

View
unanswered posts

Logged in as dmfraser66.

The Dynaco Tube Audio Forum

Basket

Go to page : 1, 2,
3

Dynaco ST-70 PC-3 driver board parts layout - photo ...

Share

Bob
Latino

View
the profile

Private
Message

Send
e-mail

See
all posts

Bob
Latino

Admin

Posts: 2043
Join date: 2008-11-26
Location: Massachusetts

Post n°1

Dynaco
ST-70 PC-3 driver board parts layout - photo ...

by Bob Latino on Wed Nov
04, 2009 8:43 am

Dynaco never
gave a parts layout on their PC-3 driver board for the ST-70. They also never
listed the parts that were on the driver board in the main parts list for the
amp on page 11 of the ST-70 assembly manual. All they said in the parts list
on page 11 was that you got a "Printed Circuit Assembly - PC-3 part #557003".
When you got your ST-70 kit the driver board was already preassembled. In the
photo below you can see the value of every resistor and capacitor on the PC-3.
The photo is of one of the fiberglass PC-3 boards that Dynaco started using in
the last few years of production. If you have one of the older "brown" PC-3
driver boards, the parts layout is
identical.

Bob

Hirak

View
the profile

Private
Message

See
all posts

Hirak

Posts: 1
Join date: 2009-11-06

Post n°2

TC-7510
PCB

by Hirak
on Fri Nov 06, 2009 7:58 am

Thanks very much for the picture. I just obtained a ST-70A sans EL-34s
(the seller would not include these!) and I am looking to replace the quad can
and the caps on this board. I assume I would replace the same values but opt
for higher voltages? Any recommendations on capacitor quality (brand) and
voltages?
Thanks!

Bob
Latino

View
the profile

Private
Message

Send
e-mail

See
all posts

Bob
Latino

Admin

Posts: 2043
Join date: 2008-11-26
Location: Massachusetts

Post n°3

Re:
Dynaco ST-70 PC-3 driver board parts layout - photo ...

by Bob Latino on Fri Nov
06, 2009 10:25 am

Hirak wrote:Thanks very much for the picture. I just
obtained a ST-70A sans EL-34s (the seller would not include these!) and I am
looking to replace the quad can and the caps on this board. I assume I would
replace the same values but opt for higher voltages? Any recommendations on
capacitor quality (brand) and
voltages?
Thanks!

Hirak,

The BEST can capacitor you can put in there as a replacement quad cap for the
ST-70 is the Dynakitparts 80, 40, 30, 20 uF 550 rated volt quad cap. Kevin at
Dynakitparts has them made by F&T capacitors in Germany. I use one in my own
ST-70. They are $60 each but worth it in the long run. When you install this cap
just have the "80" section face the back of the amp and all the other sections
will be in the correct position. This cap has almost double the DC power storage
of the original Dynaco quad cap.

Dynakiparts 550 volt rated quad cap

As
for cap sizes > With the four main coupling caps on this board (which are .10
uF @ 400 volts), you can go up to .22 @ 400 volts or .22 @ 600 volts. On the two
.05 @ 400 volt caps that are beside the two tube sockets you can go up to .10 @
400 volts. Nice caps for the money in both positions (and caps that will fit the
two positions very well) are the SBE 716P "orange drop" caps. Antique Electronic
Supply sells these. If you plan to replace EVERYTHING on an original driver
board IMHO you are probably better off just getting a NEW DRIVER BOARD AND PARTS
SET from Dynakitparts with metal film resistors.($50) Metal film resistors hold
their tolerance a lot better than the old carbon composition resistors as found
on the original ST-70 board and are nearly always quieter. The parts set with
this board includes 600 volt rated capacitors.

Bob

Last edited by Bob Latino on Thu Jul 07, 2011
10:20 am; edited 2 times in total

scsidude2

View
the profile

Private
Message

See
all posts

scsidude2

Posts: 21
Join date: 2010-03-19
Age: 28
Location: Dekalb, IL

Post n°4

Re:
Dynaco ST-70 PC-3 driver board parts layout - photo ...

by scsidude2
on Fri Mar 19, 2010 2:11 pm

First of all thank you for the picture, it has been very helpful in my
rebuilding project. I was wondering, though, if there are any side effects to
moving to .22uF at 600 volts from .1uF at 400 volts? Thank you! -Ryan

Bob
Latino

View
the profile

Private
Message

Send
e-mail

See
all posts

Bob
Latino

Admin

Posts: 2043
Join date: 2008-11-26
Location: Massachusetts

Post n°5

Re:
Dynaco ST-70 PC-3 driver board parts layout - photo ...

by Bob Latino on Fri Mar
19, 2010 2:33 pm

scsidude2 wrote:First of all thank you for the picture, it
has been very helpful in my rebuilding project. I was wondering, though, if
there are any side effects to moving to .22uF at 600 volts from .1uF at 400
volts? Thank you! -Ryan

Hi
Ryan,

No side effects that I have seen. The 4 main coupling caps on the
ST-70 "should have been" (IMHO) .22 uF @ 600 volts. Dynaco saved a few cents on
each amp by using the .10 uF @ 400 volts. I think the .22 uF cap may also help
give a stock amp a little better bass response and the 600 volts cap will stand
up a little better to the high voltage on one side of the cap.

The only
minor disadvantage is that many .22 uF @ 600 volt caps will be a little larger.
Nice caps for the money that would work here are the SBE 716P .22 @ 600 volt
"orange drop" caps sold by Antique Electronic Supply. They are larger than the
stock caps but will fit OK onto a stock board. You just bend the leads to fit
.They are $2.36 each. Small photo below of these caps below ...

Bob

scsidude2

View
the profile

Private
Message

See
all posts

scsidude2

Posts: 21
Join date: 2010-03-19
Age: 28
Location: Dekalb, IL

Post n°6

Re:
Dynaco ST-70 PC-3 driver board parts layout - photo ...

by scsidude2
on Sat Mar 20, 2010 8:15 am

Thank you for your quick and thorough response Bob, you answered my
question completely. I do have one last question though, which is what voltage
the 390pF Caps run at? I've seen them for both 1000v and 500v. Thanks!
-Ryan

Bob
Latino

View
the profile

Private
Message

Send
e-mail

See
all posts

Bob
Latino

Admin

Posts: 2043
Join date: 2008-11-26
Location: Massachusetts

Post n°7

Re:
Dynaco ST-70 PC-3 driver board parts layout - photo ...

by Bob Latino on Sat Mar
20, 2010 8:20 am

scsidude2 wrote:Thank you for your quick and thorough
response Bob, you answered my question completely. I do have one last question
though, which is what voltage the 390pF Caps run at? I've seen them for both
1000v and 500v. Thanks! -Ryan

Ryan,

For the 390 pF cap a 500 volt rated cap is more than enough. A silver mica cap
IMHO is best here.

Bob

scsidude2

View
the profile

Private
Message

See
all posts

scsidude2

Posts: 21
Join date: 2010-03-19
Age: 28
Location: Dekalb, IL

Post n°8

Re:
Dynaco ST-70 PC-3 driver board parts layout - photo ...

by scsidude2
on Sat Mar 27, 2010 3:02 pm

Thanks for all the help Bob, i just installed the new caps and it sounds
great! I was wondering what your recommendation was for the two 50 MFD caps on
the terminal strip under the right channel output transformer as to what would
be a good upgrade for them? Thanks again! -Ryan

Bob
Latino

View
the profile

Private
Message

Send
e-mail

See
all posts

Bob
Latino

Admin

Posts: 2043
Join date: 2008-11-26
Location: Massachusetts

Post n°9

Re:
Dynaco ST-70 PC-3 driver board parts layout - photo ...

by Bob Latino on Sat Mar
27, 2010 3:27 pm

scsidude2 wrote:Thanks for all the help Bob, i just
installed the new caps and it sounds great! I was wondering what your
recommendation was for the two 50 MFD caps on the terminal strip under the
right channel output transformer as to what would be a good upgrade for them?
Thanks again! -Ryan

Hi
Ryan,

I think you mean the 7 lug terminal strip under the LEFT output
transformer.

Those 50 uF caps on the 7 lug terminal strip are only
looking at maybe 70 VDC. Any two 47 to 50 uF electrolytic caps at 100 volts or
higher would work fine here. Just make sure that you have the polarity correct
on these two caps. The "+" end of each cap goes to lug 1 and on the two "-"
ends, one goes to lug 3 and one to lug 4. See pictorial below
...
Bob

sventube

View
the profile

Private
Message

See
all posts

sventube

Posts: 1
Join date: 2010-02-22

Post n°10

VTA
with Quad cap

by sventube
on Mon Mar 29, 2010 2:44 am

Bob : I just purchased the VTA board from Roy . Can I use the F+T quad cap
you recommend 80,40,30,20 ?

Thanks, Sventube

Bob
Latino

View
the profile

Private
Message

Send
e-mail

See
all posts

Bob
Latino

Admin

Posts: 2043
Join date: 2008-11-26
Location: Massachusetts

Post n°11

Re:
Dynaco ST-70 PC-3 driver board parts layout - photo ...

by Bob Latino on Mon Mar
29, 2010 2:49 am

sventube wrote:Bob : I just purchased the VTA board from Roy
. Can I use the F+T quad cap you recommend 80,40,30,20 ?

Thanks,
Sventube

Hi
Sventube,

Yes - You can ... When you put the F&T cap in there to
replace the original quad cap just make sure that the "80" section faces the
back of the amp. If you do that then all the other sections will be properly
oriented.

Bob

Kuma

Kuma

Guest

Post n°12

Dynaco
cap installation

by Kuma on Mon Mar 29, 2010
4:59 pm

I plan on replacing the entire board when funds become available - but in
the meantime, it's nice to hear your expert commentary on upgrading the
original. I just ordered the 716p Orange Drops and Silver Mica caps at your
recommended values.

Thank you very much for providing this
information.

Bob
Latino

View
the profile

Private
Message

Send
e-mail

See
all posts

Bob
Latino

Admin

Posts: 2043
Join date: 2008-11-26
Location: Massachusetts

Post n°13

Re:
Dynaco ST-70 PC-3 driver board parts layout - photo ...

by Bob Latino on Mon Mar
29, 2010 5:19 pm

Kuma wrote:I plan on replacing the entire board when funds
become available - but in the meantime, it's nice to hear your expert
commentary on upgrading the original. I just ordered the 716p Orange Drops
and Silver Mica caps at your recommended values.

Thank you very much
for providing this information.

Hi
Kuma,

The 716P "orange drop" caps are large and will stick up higher
than the stock caps. Just bend the leads to fit the holes in the driver
board.

If you do ever replace the stock board IMHO it is best not to use
the stock circuit. The stock circuit with 7199 tubes is not linear at all drive
levels. 7199 tubes are also extinct. No one makes them anymore. The only source
of these tubes is what is in circulation right now. IMHO if you do replace your
driver board at some time in the future, you would be better off to use one of
the VTA upgraded driver boards. It has a number of advantages over the stock
driver board like ..

1. Individual bias controls for each output tube and
an "on board" bias system
2. No open solder traces and all eyelets have
plated through holes so that components may be placed on the top or the bottom
of the board.
3. An "on board" power supply so that the board components
don't have to pull B+ high voltage from the quad cap (or underchassis power
board)
4. The VTA driver board uses easy to source 12AT7 tubes (standard gain
board) or 12AU7 tubes (lower gain board)

Bob

vleena

View
the profile

Private
Message

See
all posts

vleena

Posts: 9
Join date: 2010-01-22

Post n°14

Re:
Dynaco ST-70 PC-3 driver board parts layout - photo ...

by vleena
on Mon May 31, 2010 6:10 pm

Hi Bob,
Beside my ST-35, I just purchased a ST-70 with original PC
board. (latest version as you described above), I am thinking of replacing the
original BalckCat coupling caps with PIO caps, namely Jensen. As I expect
sweeter, mellow and warmer sound from them. Any other options. Shall I go
for.22 (4 units) amd .1 (2 units)? How Jensen compared to Orange Drop 716P
?

thanks

Bob
Latino

View
the profile

Private
Message

Send
e-mail

See
all posts

Bob
Latino

Admin

Posts: 2043
Join date: 2008-11-26
Location: Massachusetts

Post n°15

Re:
Dynaco ST-70 PC-3 driver board parts layout - photo ...

by Bob Latino on Mon May
31, 2010 6:19 pm

Hi,

Jensen makes a few different types of audio capacitors. I have never personally
heard any of them so cannot comment on their sound. The 716P orange drop caps
are very good caps and are inexpensive at $1.50 - $2.00 per cap. I would go one
size up as you mentioned with four .22 uF caps and two .10 uF
caps.

Bob

« View
previous topic · View
next topic »

Go to page : 1, 2,
3

Quick reply

Select a forum||--Basket|--Dynaco photos    |--Your Dynaco
sytem

Current date/time is Mon Mar 16, 2015 2:44 pm

Free forums | Invision | Free forum support | Contact | Report an abuse