First build troubleshooting

[geoff 1965]

you could do that,your voltages look to be in the ballpark so what is it exactly that you don't like about the amp?is it simply the lack of preamp overdrive?
which speaker are you using?
these amps take pedals well so you could keep the tremolo channel and use a boost as an option.

[9voltchicken]

you could do that,your voltages look to be in the ballpark so what is it exactly that you don't like about the amp?is it simply the lack of preamp overdrive?
which speaker are you using?
these amps take pedals well so you could keep the tremolo channel and use a boost as an option.

I guess I'm slowly coming to realize that the problem with this amplifier may very well be my expectations and ignorance. I have much more experience with contemporary amplifiers in how they behave. In contrast, an amplifier with dedicated inputs like this is something I rarely have a chance to interact with. This amp was described to have a cleaner tremolo channel and a dirtier normal channel with "plenty of early break up". Both channels, to me, sound identical. There is some difference between high/low inputs on each channel but this amplifier does not start to break up until I'm digging into the strings past 6 with moderate output humbuckers. In short; less tonal variety than I was expecting.

It came with an unmarked speaker assumed to be a Mojotone BV-30V, supposedly a clone of a Celestion V30. It does sound pretty good. I do have a Tone Tubby Humboldt ceramic kicking around somewhere I may try at some point once it's deemed to be working properly.

[Daviedawg]

Can I describe my original 18 watt in respect of your findings. It is a common issue to interpret descriptions of amp performance but here we go.
The normal channel as built originally had two inputs with the same tone. I modified that to have a single and a parallel inputs. Now the tone from each is different. Volume is up on the parallel a small proportion. Tone is thicker. Both break up from 3 of 10 on the vol dial at which point they are crunchy getting to creamy by 6. I rarely go beyond that. The break up point and amount varies with guitars of course.
The tremolo channel is brighter with the hi significantly louder than the lo input. Both break up at 3 of 10. This channel does not go creamy like the normal but gets a little louder all the way with more "distortion". Mostly I use it around 3 on the dial. But it varies with guitars. Old PAFs sound superb at 3 onwards.
I would not describe either channel as cleaner. But if I want clean I keep the trem channel vol to 1 or 2.
My view has always been that the biasing of the power valves is a major factor in getting that 18 watt tone. Your cathode voltage is 11.5 so it should be ok. 12v is the ideal. The value of the cathode resistor sets that voltage. Mine is 125 ohms but it can vary.

Dd

Edit: that is all through a pair of Celestion V10 30s presenting 8 ohms.

[JMPGuitars]

Both channels, to me, sound identical. There is some difference between high/low inputs on each channel but this amplifier does not start to break up until I'm digging into the strings past 6 with moderate output humbuckers. In short; less tonal variety than I was expecting.

It came with an unmarked speaker assumed to be a Mojotone BV-30V, supposedly a clone of a Celestion V30. It does sound pretty good. I do have a Tone Tubby Humboldt ceramic kicking around somewhere I may try at some point once it's deemed to be working properly.

I see two problems here:

1. Ditch the speaker and throw the Humbolt in there, and make sure to post a demo...I've been wanting to hear one of those in an 18watter. Personally, I think V30s sound terrible in this amp.

2. Before you make your demo, get your B+ down. 357 is too high. High B+ is going give you too much headroom. The ideal B+ is between 340 to 345. I usually use 340 as a target. That's why you're not getting the tasty overdrive at lower volume levels.

Thanks,
Josh

[9voltchicken]

I see two problems here:

1. Ditch the speaker and throw the Humbolt in there, and make sure to post a demo...I've been wanting to hear one of those in an 18watter. Personally, I think V30s sound terrible in this amp.

2. Before you make your demo, get your B+ down. 357 is too high. High B+ is going give you too much headroom. The ideal B+ is between 340 to 345. I usually use 340 as a target. That's why you're not getting the tasty overdrive at lower volume levels.

Thanks,
Josh

I'd be happy to post a demo once I get this amp all together. I'll even do an A/B with the stock speaker just for contrast.
What is the best way to go about dropping the voltages down a bit? I've seen suggestions of in-line resistors between the rectifier and filter capacitor as well as Zener diodes.

Thank you for the description of your amp DD, that helped my perspective quite a bit.

[JMPGuitars]

I'd be happy to post a demo once I get this amp all together. I'll even do an A/B with the stock speaker just for contrast.
What is the best way to go about dropping the voltages down a bit? I've seen suggestions of in-line resistors between the rectifier and filter capacitor as well as Zener diodes.

Thank you for the description of your amp DD, that helped my perspective quite a bit.

You want to drop around 15 volts. A dropping resistor or zener diode would work (usually I think people heatsink the zeners).

this thread for more info (including math): viewtopic.php?f=4&t=25314&p=242225&hili ... ng#p242225

You can also do a search for using a zener diode.

Thanks,
Josh

[9voltchicken]

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