45s in steromour II ?
- Thread starter lordvader
- Start date
Natural Sound
New member
It is interesting that there is no mention of running the Stereomour II with 45 tubes. I'm sure it can. The main differences between the I and II are the universal power transformer and a second 12AT7 to add two triode sections that will be used in future upgrades. But lets wait for someone at Bottlehead HQ to give the official answer.
http://bottlehead.com/smf/index.php?topic=7804.msg75442#msg75442
PB's answer to this question from the launch/intro thread. SPOILER: the answer is yes.
PB's answer to this question from the launch/intro thread. SPOILER: the answer is yes.
Natural Sound
New member
Thanks Brent!
Paul Joppa
Moderator
We have not yet generated a description for how to make the change, but we did allow for the possibility in the design phase. We decided to leave it out of the manual because relatively few make the change, and it just adds confusion for the many who don't.
Natural Sound
New member
Paul Joppa said:
Makes sense, Paul. Will the conversion instructions be made available on the forum via a "sticky" or something? I haven't pulled the trigger on a Stereomour II yet. I'm waiting a little to see what you guys have in mind for the upgrade goodies. Chances are good that I'll be trying the amp in both configurations since I have a nice stash of 2A3 and 45 tubes.
The Kaiju will not have a 2A3 or 45 option.
Just to clarify the Kaiju 300B amp is, in single ended tube terms, a high power amp. The Stereomour II is a lower powered SE tube amp, and a 45 wants to live in a Stereomour II. There is not really any point in putting an Aprilia RSV4 engine in an Alfa Romeo 4C. It will work a lot better in an Aprilia.
K
kevner21
Guest
to give some incentive to the designers I wont buy a stereomour 2 until you can convert it to #45 tubes, lol from the time PJ found the error in the 45 conversion in another topic , I have just been thrilled with my stereomour 45
Paul Joppa
Moderator
The ability to convert to 45s is built into the design, we just haven't written instructions yet. It is as simple as the original - swapping out a few resistors and exchanging a couple plate choke wires. We left out the instructions in the main manual to reduce confusion.
K
kevner21
Guest
no , I'm in no hurry to get the stereomur 2 , I'm just in disbelief that 1.75wpc is making such wonderful sound after 40 of spending thousands of dollars foolishly to get nothing even close to this. which has been around in radios 70, 80 years. cant get over it, and again thank you, thank you, thank you!!!!!!!!!!!!!!!!!
rockdoc
New member
lordvader said:So what do I need to do to get this working ?
My Stereomour II should be arriving any day now
I'm really curious about this too. I really prefer 45s, and am looking forward to building one of these. Would this mod use the same output transformers as for the 2a3? What is the impedance on the OTs in the kit?
rockdoc
Paul Joppa
Moderator
The output transformers in Stereomour II are 4K ohms, and will run with 45s very well.
Conversion to the 45 is moderately simple, but there are a few non-obvious things involved. Some of the resistor values must change, and to confirm the right value we'll have to make the changes ourselves and measure the results. I THINK this is the list of changes:
Reduce power supply voltage (increase the 130-ohm 2-watt resistors)
Adjust the filament voltage (increase the 0.15 ohm resistors)
Change the cathode bias resistors
Use the higher-inductance tap on the plate choke
[Replace the parafeed output cap - optional]
Incidentally, I originally designed it to have some other output stage options, not just the 45. It's not clear which of them we might support, at what level of support. So I won't say more just yet.
Conversion to the 45 is moderately simple, but there are a few non-obvious things involved. Some of the resistor values must change, and to confirm the right value we'll have to make the changes ourselves and measure the results. I THINK this is the list of changes:
Reduce power supply voltage (increase the 130-ohm 2-watt resistors)
Adjust the filament voltage (increase the 0.15 ohm resistors)
Change the cathode bias resistors
Use the higher-inductance tap on the plate choke
[Replace the parafeed output cap - optional]
Incidentally, I originally designed it to have some other output stage options, not just the 45. It's not clear which of them we might support, at what level of support. So I won't say more just yet.
Paul Joppa
Moderator
The target operating point for the 2A3 in Stereomour is 300v plate to cathode, 50mA plate current, and 60v bias.
The 45 should run 275v, 35mA, 56v bias. Be aware that at the reduced current, the PSU voltage will increase slightly.
The 45 should run 275v, 35mA, 56v bias. Be aware that at the reduced current, the PSU voltage will increase slightly.
