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Hi All,
Recently completed upgrade to PAS 2 phono stage. Assembled and wired up, sound is good but volume very low. Like 2.5 out of 10 low when turned all the way up. Sound is good, not distorted. Line stage volume is ok. Previous phono board worked well.
Any ideas why I may be having volume issues? I will recheck all connects and layout. Any troubleshooting wisdom welcome.
Thanks in advance for any suggestions,
Thanks
K
Follow Ups:
apparently the upgraded power supply in the PAS was not sufficiently upgraded for the new phono and line stages. Fortunately I had purchased a new PS, but was installing one component at a time to monitor incremental changes - no go.
Installed the new PS and all is well.
Thanks again for all the helpful input from this consistently thoughtful and helpful community!!
K
A different tube type will mess every parameter up of an RIAA phonostage.
as an aftermarket PC6 (phono stage) replacement for the PAS using 12AY7s in place of the original 12AX7 Dynaco design.
Thanks,
K
I have searched the internet and I cannot find an aftermarket PC6 designed to use 12ay7.
Could you share?
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Kit #7 PH-10 uses 12ay7 tubes. There may be others but I am
familiar with this one.
Also, it has a FET for more gain capability.
.
Have Fun and Enjoy the Music
"Still Working the Problem"
The PC6 is designed for 12ax7, the powersupply won't take the additional
load 9from 12ay7.
So your best option is to install 12ax7 in the pc6 board.
A 12AY7 only has a gain of 40, whereas a 12AX7 has a gain of 100. Are you aware of that? Ray
"...the fool doth think he is wise but the wise man knows himself to be nothing but a fool." Will Shakespeare
Hi,
Yes, actually I am aware of that..
So would the point be that the higher gain of the 12AX might allow it to function with the lower voltage and sound "normal" whereas the 12AY
would struggle, resulting in an obvious decrement in performance?
Thanks,
Kevin
What happens if you put 12ax7's in?
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
They are different tubes. The Dynaco boards were designed to work with a 12AX7 and it's active feedback RIAA compensation needs all the gain to work the EQ task which is quite a mountain to climb. You should follow the recommendations that dynaco issued for B+ voltage. Maybe you have a power supply problem. Many of these early 12ax7 feedback circuits ran them low PLATE current, around 1MA, which starved the tube. Generally if you change one thing you have to wind up changing many other things to compensate.
"...the fool doth think he is wise but the wise man knows himself to be nothing but a fool." Will Shakespeare
I don't disagree with anything you wrote, except I had not thought of 1mA as being a detrimentally low current for a 12AX7. Many designs seem to use that amount of current, more or less.
There's only about 200v coming off the power supply, and the schematic calls for 250-280v depending on which one I'm looking at. There are other lowered readings around the board, but I'd guess they're related to the upstream issue.
I guess that the lower PS output could be the culprit, though it's odd that it didn't result in any diminished output on the original phono board.
K
Thanks for the suggestions:
I will re-check connections and layout
Yes- 12 AY7, two new pair
I do have a schematic (-though I'm not esp.skilled at reading them!)
I will try to track down some of the voltages shown (carefully) on
the board and report back.
Thanks again to all, this board is always a great resource!
Kevin
Have you reinstalled 12AU7s instead of 12AX7s ? Lower mu ??
Jeff Medwin
Have you checked your plate and bias voltages on the phono tubes? Use your DMM to check those numbers. If those numbers are good maybe your rca jacks need to be cleaned also your selector switch. good luck, dak
Sounds like something could be shorting to ground but then after thinking about it there would probably be no sound. I would go over the wiring with a fine tooth comb and check all your soldering joints. Check all the voltages and compare it to the schematic.
You have the schemo with voltage readings? Maybe a good place to start.
Are the resistors and hookups from the input jack to the input stage correct?
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