Turning a Seduction tape pre back to Seduction phono!

[AstromanoftheFuture]

So a buddy of mine impulse bought a used Seduction that had been converted for reel-to-reel use. Even before receiving it he found out the gain would be a little suboptimal for his player, so he decided to pass it on. I think I’d like to convert it back to a phono pre. It might be due for a bit of refurbishment anyways, I’m not sure how old this is (other than knowing roughly the time period the kit was available)
I’ll email about getting a manual, and I’m currently looking at the archived post of how to do the tape conversion to get a feel for what was changed in the first place (and to see if this particular unit lines up with that)

 

[Paul Joppa]

That's an old one! The PT-1 power transformer was introduced in 2003 and the last batch was ordered at the beginning of 2012. I see some upgraded capacitors in there.

It will "work" with a phono cartridge, though with a messed-up frequency response. You may want to try it, just to see if it is in working condition before modifying the equalization to RIAA.

 

[debk]

That is very cool a walk down memory lane.  The seduction was the first BH kit I built

Debra

 

[2wo]

My  nephew ran off with mine he's still using it...John

 

[AstromanoftheFuture]

I contacted Eileen and I now have the manual and associated ephemera to try to take this back to phono usage. More to come,TBD

 

[AstromanoftheFuture]

So I needed to turn the Seduction back to RIAA, and I found this old post showing some slightly different parts values that what the kit originally came with:

http://www.bottlehead.com/smf/index.php/topic,1079.msg9382.html#msg9382

If you don't want to follow the link, basically Paul Joppa said to:

Change the 66.5K resistor to 73.2K 1%
Change the 9.64K resistor to 10.5K 1%
Change the 0.033uF capacitor to 0.030uF
Change the (0.010+0.0012uF) capacitor to 0.010uF

So I ordered some parts from Mouser, Vishay Dale resistors, and panasonic caps for the 0.03uF value (not a common value to find). For the 0.010uF caps I already had some Cornell Dubilier 940C series on hand (though in retrospect, I should have used something physically smaller than those.

After changing things out, I ran voltage checks... and some things don't check out. PJ said in his earlier response "you may want to try it, just to see if it is in working condition before modifying the equalization..." --wise words. Of course, I may have screwed something up in my frontier medicine style surgery that I just performed.

My voltage readings last night:
Terminal 6 expected 6.5vdc observed 6.8vdc
Terminal 9 expected 6vdc observed 6.06vdc
Terminal 12 expected 135vdc observed 123.5vdc
Terminal 15 expected 148vdc observed 148.2vdc
Terminal 25 expected 160vdc observed 159.2vdc
Terminal 27,37 expected 70vdc observed 70.2 and 61.7
Terminal 29,39 expected 70vdc observed 69.6 and 61.2
Terminal 30,40 expected 70vdc observed 69.6 and 61.2
Terminal 34,44 expected 135vdc observed 123.2 and 123.3
A1,B1 expected 70vdc observed 67.9 and 60.1
A3,B3 expected 1.6vdc observed 1.563 and 1.558vdc
A5,B5 expected 6vdc observed 6.06 and 6.06vdc
A6,B6 expected 70vdc observed 69.6 and 61.1
A8,B8 expected 1.6vdc observed 1.584 and 1.582

This was late last night, and I have yet to stare at the path of components to try to figure out what's going on with that one channel.

 

[Paul Birkeland]

Do you have the C4S board in this preamp or the 18K plate loads?

 

[AstromanoftheFuture]

It has the C4S board

 

[Paul Birkeland]

What specific tubes are in it?  Those voltages aren't exactly the end of the world, and voltages on the low side could indicate a lot of emission, not necessarily other issues.

 

[AstromanoftheFuture]

Specifically it has Tekefunken E88CC-TK (6922?)

 

[Paul Birkeland]

There may not be anything to sort out with those voltages, I wouldn't be too concerned.

 

[Paul Joppa]

You can swap the tubes and see if the 60v/70v swaps sides. That would confirm its just variation between tubes.

 

[AstromanoftheFuture]

I was actually thinking to try that, thanks!

 

[AstromanoftheFuture]

You can swap the tubes and see if the 60v/70v swaps sides. That would confirm its just variation between tubes.

Swapping the tubes does indeed bring about that exact result