Stereomour 45 Voltage Question

[ptlud]

I just finished building the Stereomour for 45 tubes.   I substituted 4.7 uF Mundorf Supremes for the 3.3 uF Solens.

T1  357V
T15 355V
T17 366V
T19 364V
A2 356V
C2 354V
IA 364V
IB 366V

The amps is running great, but I want to make sure there isn't something wrong with the wiring.

Thanks,

Paul

[Paul Joppa]

I think there may be a problem in the manual. More after I check with the rest of the team.

[ptlud]

I re-checked the wiring and think the amp is correctly wired for the 45 tube.  The voltage values I measured are within ~ 5% of nominal.

Paul

[Paul Joppa]

OK, I've checked my analysis again and I'm sure about this.

There is an error in the manual (both 2010 and 2014 versions) on page 50, wiring the plate choke for the 45. Doc B will put up a sticky post soon, but meanwhile here is what you need to know:

The blue wire should go to the 45 socket pin 2, for both 45 and 2A3.

For the 45, the black (sometimes black/red) wires go to  terminal 17L and 19L - this is their parking spot since they are not connected to anything else.

For the 45, the red wires go to the HV+ terminals on the power supply board (see p.54, where the 2A3 configuration is shown - but for the 45, put the RED wire in the HV+ center hole). This will greatly improve the bass.

Sorry we missed this for so long - not many have done the 45 conversion, and I caught it by accident when I saw you had only 10 volts drop across the choke. It should be 30 volts drop, so your 45 plate voltage will drop by 20 volts, putting it much closer to the correct voltage. This same voltage error appears in the voltage checks; A2 and C2 should be listed as 320v, not 340v.

[ptlud]

OK I made the changes (see attached photo).  Here are the new voltages.

T1 345V
T15 337V
T16 55V
T17 354V
T19 355V
T20 54V
A2 334V
C2 336V
IA 364V
IB 363V
These voltages are much closer, except IA and IB.

Please let me know if its OK to use the amp.

Paul

[Paul Joppa]

Looks really good - try some tunes!

[ptlud]

Playing JJ Johnson Standards CD.  Sounds great.  Not sure I can tell the difference, but I am glad the 45's are being run at the right voltage.  They are rather expensive.

Paul, thanks for your help and very prompt response.

Paul

[jimiclow]

OK, I've checked my analysis again and I'm sure about this.

There is an error in the manual (both 2010 and 2014 versions) on page 50, wiring the plate choke for the 45. Doc B will put up a sticky post soon, but meanwhile here is what you need to know:

The blue wire should go to the 45 socket pin 2, for both 45 and 2A3.

For the 45, the black (sometimes black/red) wires go to  terminal 17L and 19L - this is their parking spot since they are not connected to anything else.

For the 45, the red wires go to the HV+ terminals on the power supply board (see p.54, where the 2A3 configuration is shown - but for the 45, put the RED wire in the HV+ center hole). This will greatly improve the bass.

Sorry we missed this for so long - not many have done the 45 conversion, and I caught it by accident when I saw you had only 10 volts drop across the choke. It should be 30 volts drop, so your 45 plate voltage will drop by 20 volts, putting it much closer to the correct voltage. This same voltage error appears in the voltage checks; A2 and C2 should be listed as 320v, not 340v.

Paul, so is this the reason my Stereomour was dissipating 11.25 watts because of the extra 20 volts? Thanks for the info.

[Paul Joppa]

Paul, so is this the reason my Stereomour was dissipating 11.25 watts because of the extra 20 volts? Thanks for the info.

Yes, I believe that is most of the reason. I'm bummed that we missed that clue for so long. Try the switch - you will find a change in the deep bass, and I believe you will like it.

[jimiclow]

Paul, you're right! I swapped the wires this morning, not only more bass but better sound. But then I'm now using the Smash. I've been listening to the old configuration for almost 2 years, didn't know it could be improved with just a wire swap.
Thanks Paul!

[rusty-jade]

I was going to change the circuit from a 45 back to a 2A3 until I read PJ's comments.  I changed the wiring and was pleasantly surprised to hear how strong and tight the bass has become.  So, instead to reconverting the Stereomour back to 2A3,  I sold my Magellan VI sub instead!

[kevner21]

i did the conversion about 6 monthes ago and was very happy with it . never checked the voltages for such a simple changeover. the tubes acted normal except for one 45 that went south. so this is the other wire that is twisted with the blue wire that goes to the HV+?

[Paul Birkeland]

so this is the other wire that is twisted with the blue wire that goes to the HV+?

The red wire that comes from the choke should go to B+ and the blue wire from the choke goes to plate.  The black choke wires can be heatshrunk and left alone, or can anchor at the empty two terminal strip lugs on the 5 pin strip behind the 9 pin socket.

[kevner21]

Thanks CB got it now. has been playing awhile and just today changed it out for one of my other amps. to give it a rest . this amp with the 45's is quite possibly the finest ive heard. so it will be even better? cant imagine, will change it out tomorrow! thanks for the quick respond

[kevner21]

a couple questions, did I hurt anything having it wired wrong? is this only going to help the bass or is it an overall improvement? didn't listen enough yet. is the reason for this amp sounding so good, the  lack of noise and hum or is it the 45 tube , and your going to say both. and this tube was discontinued way back when , WHY? 1.75watts?