jgab
Well-Known Member
This is my first super lead, so I am looking for some info on the board and what is the standard maintenance you guys do. I have a bunch of Iskra and Piher spares so I will use NOS/OEM parts to keep this looking original.
I am thinking of replacing the following:
- 27k bias resistor ahead of the diode with a 1/2 watt Piher. Current resistor is obviously not original. Terrible replacement job too. Lazy tech. This was replaced twice as seen by the carbon film and then flame proof resistors in the different photos. Don't ask, its a bit of a story.
- 10uf bias caps with a couple new Sprague 10uf/150vdc. These blue bias caps look original to me, but not 100% sure.
- Should I replace the bias pot? Is the one in the board reliable? I have some black plastic Piher 22K.
- Should I replace the V1 330uf cathode bypass cap? Does this usually need replacing?
- Weird soldering on a couple 68K grid resistors (second photo). I will clean that up a bit. Make sure the connections under the board are good. Again, lazy tech style.
- What is that huge blue cap on the left? It is 0.047uf / 1000 vdc. Is this necessary? I have seen some super lead boards with and some without this cap.
Everything else looks pretty solid to me. I measured what I could without pulling leads and everything is within 10% spec.
I know these early ST1 boards are super delicate, but I have a good iron and good technique so I will be ok.
Any suggestions are more than welcome?
Thanks as always.
J
EDIT: Slowly getting there (see pics below). I am back at work so won't be able to make more changes for a while.
What I did: Cleaned up the socket wiring a bit (unnecessarily long lengths) , changed the output tube green screen resistors (they were reading way above 1K on a couple), replacement at the 27K bias resistor and bias diode, added some ISKRA 68K input resistors (had them on hand so why not), took out the polarity circuit, changed to Piher bias trimmer, found an old ceramic 4700pf for the Vol 1 (didn't have Lemco but it's close), updated 10uf bias caps with Sprague, replaced the 1M Vol 1 pot with an old one I had, and changed out the 350uf for a 3.3uf electrolytic to tighten up the bass (not pictured). I am also getting the original PT rewound by Heyboer. Seller replaced the PT with Classic Tone because they blew the bias secondary on the original, but I want the original back in there so it is getting rewound. Still on the fence with the filter caps, but I do have a fresh set. Pulled some leads on the Daily's and they all have awesome ESR and no physical signs of aging. Amp doesn't hum at all.
Updated Pic:
I am thinking of replacing the following:
- 27k bias resistor ahead of the diode with a 1/2 watt Piher. Current resistor is obviously not original. Terrible replacement job too. Lazy tech. This was replaced twice as seen by the carbon film and then flame proof resistors in the different photos. Don't ask, its a bit of a story.
- 10uf bias caps with a couple new Sprague 10uf/150vdc. These blue bias caps look original to me, but not 100% sure.
- Should I replace the bias pot? Is the one in the board reliable? I have some black plastic Piher 22K.
- Should I replace the V1 330uf cathode bypass cap? Does this usually need replacing?
- Weird soldering on a couple 68K grid resistors (second photo). I will clean that up a bit. Make sure the connections under the board are good. Again, lazy tech style.
- What is that huge blue cap on the left? It is 0.047uf / 1000 vdc. Is this necessary? I have seen some super lead boards with and some without this cap.
Everything else looks pretty solid to me. I measured what I could without pulling leads and everything is within 10% spec.
I know these early ST1 boards are super delicate, but I have a good iron and good technique so I will be ok.
Any suggestions are more than welcome?
Thanks as always.
J
EDIT: Slowly getting there (see pics below). I am back at work so won't be able to make more changes for a while.
What I did: Cleaned up the socket wiring a bit (unnecessarily long lengths) , changed the output tube green screen resistors (they were reading way above 1K on a couple), replacement at the 27K bias resistor and bias diode, added some ISKRA 68K input resistors (had them on hand so why not), took out the polarity circuit, changed to Piher bias trimmer, found an old ceramic 4700pf for the Vol 1 (didn't have Lemco but it's close), updated 10uf bias caps with Sprague, replaced the 1M Vol 1 pot with an old one I had, and changed out the 350uf for a 3.3uf electrolytic to tighten up the bass (not pictured). I am also getting the original PT rewound by Heyboer. Seller replaced the PT with Classic Tone because they blew the bias secondary on the original, but I want the original back in there so it is getting rewound. Still on the fence with the filter caps, but I do have a fresh set. Pulled some leads on the Daily's and they all have awesome ESR and no physical signs of aging. Amp doesn't hum at all.
Updated Pic:
Last edited: