Dynaco Stereo 70 Noise Issue

I have a ST-70 making awful crackle noises in the left channel only.  All tests done with no source connected.

I can easily recreate it by touching and slightly moving the 7199 tube.  Seems like the tube socket could be the culprit.  

Tube feels loose.  I re-tensioned each socket pin.  Still noise.
I reflowed the 9 pins on the bottom of the board.  Still noise.
I swapped left and right 7199 tubes.  Still noise in left channel only.

It can get so bad that just touching the chassis can generate the noise.  

I have chopstick all components in that area.  Really seems to be a fatigued tube socket.  

My questions for now are;  

anything else to check?
recommended sources for a replacement socket?

Thank you!  MC

I would do this :
1/ clean the board , alcohol and a brush could be all that is needed

2/ reflow the solders on THE SUSPECT SIDE
See if problem goes away.
Otherwise get a new board fro dynakitparts https://www.dynakitparts.com/product-category/dynakit-products/pc-boards/
PC3A is for 7199 tube; you can reuse your 7199 tubes OR
PC3B is for 6U8 type tube, this will clear the dependency of 7199 tubes and enable a much
larger supply of tubes ( 6GH8, 6BL8 6U8 ) that will all work fine. I guess dynakitparts can
supply these too.

Changning the board is easy, it will fit exactly as the old board.

Total rebuild sounds intriguing but this is not my amp.  

I did a but more testing.  If I hold down the left 7199 at a certain angle there is no noise even with me using the chopstick all over the place.

So I am pretty convinced it needs a new tube socket.  I am interested in opinions on replacing the entire driver board with a new pre-built unit.  

I would also like to here opinions on the 7199 vs 6GH8A assembled boards.  Is there a difference in sound between the two versions?

Why is there a huge price gap between both assembled boards on https://www.dynakitparts.com/product-category/dynakit-products/pc-boards/

the assembled 7199 board PC-3A ST-70, is $72
the assembled 6GH8A board PC-3B ST-70, is $120

misterc57 wrote:Total rebuild sounds intriguing but this is not my amp.  

I did a but more testing.  If I hold down the left 7199 at a certain angle there is no noise even with me using the chopstick all over the place.

So I am pretty convinced it needs a new tube socket.  I am interested in opinions on replacing the entire driver board with a new pre-built unit.  

I would also like to here opinions on the 7199 vs 6GH8A assembled boards.  Is there a difference in sound between the two versions?

Why is there a huge price gap between both assembled boards on https://www.dynakitparts.com/product-category/dynakit-products/pc-boards/

the assembled 7199 board PC-3A ST-70, is $72
the assembled 6GH8A board PC-3B ST-70, is $120

I guess it's market talking. Very few aims to keep the 7199 due to the scaricity of these tubes,
using alternatives that allows plenty of cheap equally good tubes keeps demand higher for
these boards.

My advice is to get PC-3B including tubes and sell your 7199 on ebay for a substantional sum.

Over the years, I have read that the original board material itself can cause problems. It was alright back in the Cretaceous era, but it may have cooked itself, absorbed moisture and cycled until it is conductive somehow.

Years ago, I replaced mine with a glass board that retains the original architecture — because I had a supply of NOS 7199's.

Of course, Bob's suggestion is the best solution. But if that is not an optimal way for you to go — considering that the amp isn't yours — try to source a new stock board. Just my two bits, cuz wiggling tubes and guessing must be pretty frustrating.

I am waiting on the assembled VTA-70 board to arrive! Will let you know how it goes.

Thank you all.

Congrats ... you can't go wrong there!

And guard those 7199 tubes. Your friend can sell them. They are rare birds these days, and someone like me who still runs a stock board will definitely want them.

I'll be waiting to see the installation

Board is installed and wired.  I am not getting past the bias adjust on the left channel.  Bias should be 0.50 V but is exceeding that value quickly so I power down.

Instructions say bad wiring or bad tubes.  I know the tubes are good and I think I got the wiring correct.  I have attached pics.  Anyone see anything?

Thank you, MC

I have no bias VDC at pins 5 and 6 of each output tube.

With no output tubes installed, I have - 74 VDC at the bias anode on the new board.

misterc57 wrote:I have no bias VDC at pins 5 and 6 of each output tube.

With no output tubes installed, I have - 74 VDC at the bias anode on the new board.

With no output tubes you should have - 20-50 (adjustable ) on pin 5 och each EL34 socket
( pin 6 should not be connected )

Have you removed the old bias circuit ?

peterh wrote:

misterc57 wrote:I have no bias VDC at pins 5 and 6 of each output tube.

With no output tubes installed, I have - 74 VDC at the bias anode on the new board.

With no output tubes you should have - 20-50 (adjustable ) on pin 5 och each EL34 socket
( pin 6 should not be connected )

Have you removed the old bias circuit ?

Old bias circuit is still there but disconnected.  

The 4 white wires from the new board for the bias is connected at pin 6, where there is a 1K resistor connected to pin 5.

There is no VDC on any of the white wires.

I have attached the wiring diagram and a new pic.

Thank you

Seems to be a problem on the new board. Double check the board, follow the tap from the
transformer. One problem might be that the caps in the bias circuit is mounted in wrong polarity
or that the diode is mounted in wrong direction.

Send roy a mail .

seems this thread has been going in parallel with my personal email correspondence. Thanks to PeterH to have him email Roy @ tubes4hifi
Sharp lookers will notice that R39 was not installed. My fault. That corrected the bias problem.
Also the builder did not follow instructions with the resistors on the quad cap. (remove 6.8K and 22K and add 2.2K 3w).
That's all been taken care of now.

Roy has been a lot of help! Thank you!

Almost done. Will post pics on completion.

MC

From what I remember, the 7199 and 6gh8a are the exact same tube spec-wise, the only difference is the pin arraignment.

Final pics.  Thank you everyone for your help.  Starting another ST70 driver board upgrade this week.