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May 20, 2019, 11:38:25 am

Author Topic: Sliding in the 45's  (Read 704 times)

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Offline ALL212

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Sliding in the 45's
« on: June 18, 2018, 08:37:24 am »
I've got my Stereomour built for 2A3's but would like to shift to 45's.  I've got the June 16th, 2013 manual.

From the Manual:

Page 13 - I'll remove the 360 ohm resistors from the Power supply PCB.

Page 50 - I'll swap the plate choke blue and red wires.  Red to A2, red to C2.  Blues to 17L and 19L.

Page 66 - I'll remove the 4.7k 5W resistors from 6 and 16U, same at 10 and 20U.

but I've also found a post with corrections and I'm a bit lost there...
Blue wire  from plate choke stays - no change.

It says the black (sometimes black/red) wire's aren't used - park them at 17 and 19.  These are currently at HV+?

Here's where I'm really confused - red wires go to the HV+ terminals on the power supply board - use the HV+ Center   hole.  So I'm removing the black wires going to HV+ and using the red wires from the plate chokes in their place?

And last question - I used the third set of RCA's for pass through - just directly connected them to the selector.  I've also read I should put a 1k ohm resistor in series here?

Thank you!
Aaron Luebke

Offline Paul Birkeland

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Re: Sliding in the 45's
« Reply #1 on: June 18, 2018, 08:54:43 am »
Page 50 - I'll swap the plate choke blue and red wires.  Red to A2, red to C2.  Blues to 17L and 19L.
Swap black and red, that's a typo.
Blue wire  from plate choke stays - no change.
This is the typo.
It says the black (sometimes black/red) wire's aren't used - park them at 17 and 19.  These are currently at HV+?
Swap the black and red wires on each channel.
Here's where I'm really confused - red wires go to the HV+ terminals on the power supply board - use the HV+ Center   hole.  So I'm removing the black wires going to HV+ and using the red wires from the plate chokes in their place?
Yes.
And last question - I used the third set of RCA's for pass through - just directly connected them to the selector.  I've also read I should put a 1k ohm resistor in series here?
Not sure I'd bother with that, what's connected to the pass through?
Paul "PB" Birkeland

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Offline ALL212

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Re: Sliding in the 45's
« Reply #2 on: June 18, 2018, 09:18:51 am »
Thanks!

The pass through is feeding a Crack.  In that manner I don't even have to power up the Stereomour to use the same signal.
Aaron Luebke

Offline Paul Birkeland

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Re: Sliding in the 45's
« Reply #3 on: June 18, 2018, 09:37:36 am »
I don't think you'll need the 1K resistors.
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline ALL212

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Re: Sliding in the 45's
« Reply #4 on: June 19, 2018, 03:43:28 am »
Thanks Paul!  I'll report back when I get it done.
Aaron Luebke

Offline ALL212

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Re: Sliding in the 45's
« Reply #5 on: June 20, 2018, 03:26:41 am »
One more question?

Are all of these useable with the 45 mod done?

45 = 245 = CX345 = 145 = A245 = ER45 = EX645 = UX245 = PH245 = C-245 = 445 = SX245 = MX245 = 245-C = L45 = ER245 = DX245 = PA245 = AC45 = NX245 = X245 = T45 = G45 = NU-45
Aaron Luebke

Offline Paul Birkeland

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Re: Sliding in the 45's
« Reply #6 on: June 20, 2018, 04:47:57 am »
If they all have the same specifications as the 45 does, they should work just fine.
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline ALL212

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Re: Sliding in the 45's
« Reply #7 on: June 23, 2018, 02:57:18 am »
what just happened….? 

Tubes came in from Brent Jesse (Chicago supplier - good guy) and I warmed up the soldering iron.

I read nothing but good about the 45 tubes.  The mod took almost 15 minutes, everything checked out.  Used the headphone adapter to adjust the hum pots and just left it in for fun.  2 hours later the silly grin had yet to leave my face!

Moved in the speakers, just a pair of Boston Acoustic A60 Series I's I rehabbed.  Another hour disappears, silly grin remained.

Much less power, noticeable with these speakers, much more magic - noticeable with anything I plugged into it.

I read I can still use the 2a3's but at a reduced power level?  I would like to do some swapping and compare.  Right now I can't put a finger on the magic but it's there.

« Last Edit: June 23, 2018, 03:03:18 am by ALL212 »
Aaron Luebke

Offline Paul Joppa

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Re: Sliding in the 45's
« Reply #8 on: June 23, 2018, 09:22:43 am »
...
I read I can still use the 2a3's but at a reduced power level? ...
The original Stereomour (manuals dated Aug 23, 2010, Oct 21, 2011 and updated Feb 3, 2014) with PT-6 power transformer has 2.5v filament power, so the tubes can be swapped and still have the same filament voltage. I have not been able to locate a June 16th, 2013 manual, but check the parts list to confirm the PT-6.

The current Stereomour II (manual dated 2015; the file date I have is July 6, 2015) uses the PT-8 power transformer with 3.15v windings and uses resistors to drop to 2.5v. The resistors must be changed when switching between 45s (1.5 amps) and 2A3s (2.5 amps).
Paul Joppa

Offline Natural Sound

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Re: Sliding in the 45's
« Reply #9 on: June 23, 2018, 11:26:16 am »
Much less power, noticeable with these speakers, much more magic - noticeable with anything I plugged into it.

I had the same experience when I converted my Paramour II mono-blocks to run 45's. You wont get rock concert sound levels but the sweet midrange is hard to beat. Right now my favorite tube combination is a Philco 45 with a Raytheon 12AT7WA triple mica in front of it.

I also have a Stereomour II that I might convert one day. But honestly the standard 2A3 mode with the Shunt Regulator and MourQuiet upgrades sounds so freaking good I don't want to touch it.  ;)
« Last Edit: June 23, 2018, 11:29:45 am by Natural Sound »

Offline ALL212

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Re: Sliding in the 45's
« Reply #10 on: June 23, 2018, 02:17:51 pm »
PT-6 confirmed in my manual.  Might not even go there!

My hope is to build the II version this coming winter pending sales.  Pit a I with 45's against a II with 2a3's...
Aaron Luebke