Mojo output transformer
- Thread starter STRefugee
- Start date
67plexi
Ambassador of Amps
The stock Fender # 49969
That's a Mojo tone output transformer Black Face Princeton both are 8K primary should work fine
Blackface Princeton Output Transformer 125A10B
That's a Mojo tone output transformer Black Face Princeton both are 8K primary should work fine
Blackface Princeton Output Transformer 125A10B
Amp Mad Scientist
Ambassador of Heresy
No it is not the stock one. It's a Mojotone replacement.
67plexi
Ambassador of Amps
Mojotone transformers are made by Heyboer they are top quality
Some Heyboer 150 watt transformers they custom made for me the rusty one is a 300 watt Fender output transformer
Amp Mad Scientist
Ambassador of Heresy
Is your output transformer bad? I didn't think it was.
I thought you ordered that by accident.
Not many vendors give you specs, unless you can get the data sheet from the manufacturer.
OP
STRefugee
Well-Known Member
Yes, you are right. I ended up ordering the Hammond 1750f after browsing over tranformers for toi long, whilst looking for a reasonably priced replacement for the power transformer.
I saw £72!! and that seemed like a great price abd jumped on it not realising I hit the "buy now" button for an output transfo.
When after 4-5 days of wait it finally arrived, I could not wait to get home to fit it thinking "power transfo"
and was utterly dismayed to find I'd got this thing.But not all bad an outcome perhaps. Because that got me thinking, noticing the obvious difference in build between the 1750f and the Mojo.
Measuring the resistance and comparing, the Mojo gives around 145+ ohms and the 1750f around 97ohms.
The BJnr is known to have the tubes typically biaised too hot. But that Mojo output transfo in may actually help prevent that?
Amp Mad Scientist
Ambassador of Heresy
The bias setting is what makes it hot.Yes, you are right. I ended up ordering the Hammond 1750f after browsing over tranformers for toi long, whilst looking for a reasonably priced replacement for the power transformer.
I saw £72!! and that seemed like a great price abd jumped on it not realising I hit the "buy now" button for an output transfo.
When after 4-5 days of wait it finally arrived, I could not wait to get home to fit it thinking "power transfo"
But not all bad an outcome perhaps. Because that got me thinking, noticing the obvious difference in build between the 1750f and the Mojo.
Measuring the resistance and comparing, the Mojo gives around 145+ ohms and the 1750f around 97ohms.
The BJnr is known to have the tubes typically biaised too hot. But that Mojo output transfo in may actually help prevent that?
The hotter it runs, the better it sounds, but also
the shorter the tube life becomes.
The bias setting is a compromise.
syscokid
Ambassador of War & Peace
OP
STRefugee
Well-Known Member
Thanks for sharing this.
Interesting and mind boggling this!
The measurements I got for the resistance on each side that is Red to Blue, and Red to Brn were within a range of 145+ and 150 ohms only.
The Hammond 1750F sold as a drop-in replacement gives measurements of around 97 ohms either sides.
That diagram you share suggests readings over 4000 ohms each side.
On their site is listed MOJO772 "Blackface Princeton Output Transformer 125A10B" with diagram showing specs of 8k ohms for each side. The 7 digit ref (9962121) is different to mine (9960539).
I don't know what to figure from all that.
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Amp Mad Scientist
Ambassador of Heresy
The impedance on the data sheet indicates 4250 ohms.
The DC resistance measured on the ohm meter is 150 ohms.
Resistance (DC) and impedance (AC) is not the same thing.
Impedance is measured with a frequency (cycles per second or Hertz).
DC resistance has no frequency.
Sometimes the manufacturer will print the DCR (DC resistance) on the data sheet. (which can be helpful)
But this time they did not.
They only printed the impedance on the data sheet.
OP
STRefugee
Well-Known Member
@Amp Mad Scientist
Thank you for clarifying. Soooo much to learn!...
Thank you for clarifying. Soooo much to learn!...
67plexi
Ambassador of Amps
The transformers in the photo are all new even the rusty looking Fender
I got talked into reverse engineering the Dumble 150 watt Steel String Singer that said I have a lot of transformers in stock
OP
STRefugee
Well-Known Member
Wow! Quite a Beast! Quite a project too!
Could be great to have someone filming you from start to finish, make it in a series of YT vids for novices like myself to watch you as you progress.
Awesome!