I'm new to this forum but have been building ham radio and guitar amp kits for years. Just got the JTM45 kit built from ValveStorm (MetroAmp) using the Marstran original set transformers. I have looked through the forum and couldn't find anything specific as to proper voltages. You guys are the experts!
With all the tubes in EXCEPT the KT66's these are the voltages I getting. AC and DC values shown.
1 3 4 5 6 8 9
V1 227 1.95 3.21 3.21 233 1.95 3.21
V2 199 1.24 3.21 3.21 347 199 3.21
V3 264 48 3.21 3.21 249 48 3.21
2 4 6 9
V6 488 354 354 488
Does this look correct as they are higher than the 10% variance quoted in the build manual. Don't want to proceed with the KT66's. I've rechecked all the resistor values, wiring and it checks out. I can post pix. Thanks!
Need Voltages for new build w/Marstran Trannies
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Ineedguitars
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Re: Need Voltages for new build w/Marstran Trannies
looks fairly good. the marstan has higher voltage than the metro -55. adjust for maximum bias voltage (cold bias), install a small fuse and insert kt66s and go!
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Super 100 amps: 1202-119 & 1202-84
JTM45 RS OT JTM50 JMP50 1959/2203/34/39
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Super 100 amps: 1202-119 & 1202-84
JTM45 RS OT JTM50 JMP50 1959/2203/34/39
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ivan H
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Re: Need Voltages for new build w/Marstran Trannies
Hi, I have a hybrid amp that uses a Heyboer 784-139 OT/EL34's & a Marstran 1202-55 PT. It also has switchable rectifier/main filter, GZ34/32uf or SS/64uf using a 15k bias voltage adjusting resistor wired across the switch. I would have to wait til the weekend to give u exact voltages,but if I remember correctly the DC voltage at the main filter is about 438V in tube rec mode & 446V using the solid state rectifier (uf4007 diodes). Ur voltage will come down with the KT66's installed & vary a little according to bias. Hope this helps. Cheers
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Ineedguitars
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Re: Need Voltages for new build w/Marstran Trannies
OK thanks for your help,
The KT66's are in and I am getting 54mV on V4 and 57mV on V5. That's with the bias pot fully counter clockwise.
Is that acceptable or would you put in a higher value resistor (68K presently) to get it down? I've got a 150K 1/2 watt and a 100K 1 watt.
The KT66's are in and I am getting 54mV on V4 and 57mV on V5. That's with the bias pot fully counter clockwise.
Is that acceptable or would you put in a higher value resistor (68K presently) to get it down? I've got a 150K 1/2 watt and a 100K 1 watt.