Smashup Install / Microphonics

[Tim G.]

I ran my stock Smash for a couple weeks and decided it was time to install the Smashup upgrade.  Install went smoothly and it fired up and sounds great, hoping to get some good listening in this weekend but at least know its up and working.

Two things came up that I would like to get some input on:

1) Voltage check on the A socket side of the Kreg/B3 connection is about 5.8V and on Kreg/B6 the B side its 3.8V.  Swapped to another 6SN7 and no real change still a bit uneven and above 5V on the A side.  Is that being out of spec an issue?

2) Microphonics, these 4P1L tubes are very "chimey" I'm not hearing it while it is playing, but when turning the input selector and tapping on the top plate they ring for 10-15 seconds.  I have never really worked with any loctal tubes, is that just their nature?  I don't have any to swap out to compare but may see what I can scrounge up somewhere.

Otherwise this thing even stock was quite a step up from my well modded Foreplay.  Thanks for a great kit!

Tim

[galyons]

2) Microphonics, these 4P1L tubes are very "chimey" I'm not hearing it while it is playing, but when turning the input selector and tapping on the top plate they ring for 10-15 seconds. I have never really worked with any loctal tubes, is that just their nature?  I don't have any to swap out to compare but may see what I can scrounge up somewhere.


Tim

Nothing at all to do with being a loktal tube.  Loktal is simply the locking metal base, most loktal tubes have octal equivalents.  The 4P1L is known to be microphonic. The level varies from tube-to-tube.  Anything that sets up a resonance on the aluminum plate will set the 4P1L's to singing along.  Isolation and mass are your friends.  Several posts here about the issue.

Cheers,
Geary


 

[Tim G.]

Sure, I've got plenty of tricks to try, was just wondering if that would be considered a "normal" amount.  Thanks for the info!

Tim

[Paul Birkeland]

1) Voltage check on the A socket side of the Kreg/B3 connection is about 5.8V and on Kreg/B6 the B side its 3.8V.  Swapped to another 6SN7 and no real change still a bit uneven and above 5V on the A side.  Is that being out of spec an issue?

If all the other voltages check out, then this imbalance isn't a problem.  If OA/IB on both boards is sitting at 150V +/-1%, then the hybrid shunt regulator is working.

As far as the microphonics issue is concerned, directly heated preamps will exhibit this phenomenon.  Adding weight on top of the chassis/power transformer and squishy pads between the wood frame and your equipment rack will tend to minimize this.

[Tim G.]

Ok good, yes all the other voltages checked out just fine... the regulated voltages were spot on one side was 150.0 and the other I think was 149.9 or something very close.   I found a couple different vintages of tubes on Ebay to roll through, and will tinker with some damping, but at this point its not a big issue when just listening.  Thanks for the info!

Tim