Mojotone JCM800 50 watt output transformer
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wpaulvogel
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Mojotone JCM800 50 watt output transformer
Has anyone ever used one of these? I’m building an el34 amp and just ordered one. It should be a Heyboer. It’s got 3.7k primary which is a little high for a Marshall.
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Stevem
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Re: Mojotone JCM800 50 watt output transformer
From what I have seen with these 800s and there as built power supplies they never really reach 50 watts of RMS output even with the strongest output tubes I can find in them!
With the difference in primary impeadance you will likley see only 42 watts of clean power if I had to guess and less OT added distortion then the original 800s OTs had.
With the difference in primary impeadance you will likley see only 42 watts of clean power if I had to guess and less OT added distortion then the original 800s OTs had.
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
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wpaulvogel
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Re: Mojotone JCM800 50 watt output transformer
I have to change the story. I have the amp built and used an old output transformer I have had laying around. Its out of a Mcgohan M506 PA amp. This transformer has a rattle in it that makes "ghost" on top of the notes once it starts breaking up. Clean output is pure. I thought it could be the choke ringing or the output transformer. I couldn't get any funny traces on my scope but the guitar brought out the noise. I plugged in my dummy load and plucked the guitar and could hear it on the chassis. This morning I stethoscope around the chassis and located it on the output transformer. I pulled the end bells and shimmed the core. Now it is horrible. So I hope the transformer swap will rid the noise. I'm getting 49-50 watts RMS with this setup. I'll see what I get after the swap. Using a Hammond 272JX power transformer. It's making 401 volts on the plates at idle.
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wpaulvogel
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3 others liked this
Re: Mojotone JCM800 50 watt output transformer
Got the transformer. Checked the turns ratio and it’s actually 3.8k and change on all 3 taps. Installed it and the amp made 49 watts now and 400 volts on the plates at idle.
Man this thing sounds awesome! Played it for about an hour and I’m really satisfied and can’t hear shit!
Man this thing sounds awesome! Played it for about an hour and I’m really satisfied and can’t hear shit!
Re: Mojotone JCM800 50 watt output transformer
Good voltage/power output. (IMHO, its better to have a little higher Zout for EL34s than what Marshall put in their mid-60s amps, especially with today's EL34s.)wpaulvogel wrote: ↑Sun Dec 01, 2019 1:25 am Got the transformer. Checked the turns ratio and it’s actually 3.8k and change on all 3 taps. Installed it and the amp made 49 watts now and 400 volts on the plates at idle.
Man this thing sounds awesome! Played it for about an hour and I’m really satisfied and can’t hear shit!
He who dies with the most tubes... wins
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Stevem
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Re: Mojotone JCM800 50 watt output transformer
Good news to hear!
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
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wpaulvogel
- Posts: 430
- Joined: Wed Jan 23, 2019 3:11 am
- Location: Leesburg Georgia
- Contact:
1 others liked this
Re: Mojotone JCM800 50 watt output transformer
Here’s some pictures of the chassis. I’ve got to tolex the cabinet.
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Re: Mojotone JCM800 50 watt output transformer
Very clean build!! I bet it is loud and proud.
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wpaulvogel
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Re: Mojotone JCM800 50 watt output transformer
It is definitely loud and proud. The simplicity of it is what makes it do it so well. The first gain stage blends between coupling caps for the tone, it works awesome. The second stage has a bridged T midrange control and can scoop or boost. The high cut after the phase inverter really takes the edge off the upper harmonics nicely. It has plenty of different tones and dials easily.