Roland bolt 60 - ss preamp - tube power amp - anybody know anything about it?

[aimeovaldi]

Found one of these Roland BOLT 60 hybrid amps - short lived endeavor by Roland into tube amps around 1979 - 1984. Has anybody had any experience with these amps? Are they any good? How do they sound? Are they reliable? Any information would be appreciated. Thanks.

[mozwell]

i have heard these, back in the mid 80's, didnt sound too bad as i recall.
Jfet pre & valve phase inverter & power stage
I would check all the pre out / power amp in, send / return jacks to make sure the internal switch contacts still work ok

Not sure if its worth changing all the electrolytic caps, check them & see how they look.
Maybe pull the valves, power it on & take voltage measurements of the power supplies.

If all ok, tubes back in, & give it a blast

[aimeovaldi]

It is cheap enough that I think I will give it a whirl. It seems to work fine - head only. I appreciate the link to the service notes. The cleans are really nice, but the distortion is really brassy and harsh. The standby switch has been rewired and is now wired correctly - this was an issue with these amps. I believe that I will pull the plug and buy it. Thanks again for the feedback.

[J M Fahey]

I bet the preamp distortion will be harsh, but the beauty of having a Tube Power Amp means that using it LOUD will even out everything.

[aimeovaldi]

Never thought about it like that. I tried it out at a moderate level. The breakup was almost immediate on the disttortion channel, there didn't seem to be any build up. Just immediate ear splitting distortion. You wouldn't happen to know what the phase inverter does on this amp, it uses a 12AX7 tube.

[mozwell]

In distortion mode, there is an extra fet Q2 in the signal path, with 4 x clipper diodes & gain pot VR1
Diodes could be changed to 3mm led's, or reduce the gain of this stage by reducing the value of R10 (add a 10k in parallel ?)

But if its good clean, then use it that way, & use an external stomp box for the amount of dirt you want.

[pdf64]

The power amp (including the LTP phase splitter) looks to be the standard Fender BF type.
The standby looks a real 'doh'!
As it disconnects the plate supply, whilst the screen grid supply is left energised.

[g1]

The standby looks a real 'doh'!
As it disconnects the plate supply, whilst the screen grid supply is left energised.

There was some discussion of the standby mod here:
http://music-electronics-forum.com/t37621-4/#post371196

[aimeovaldi]

Just ran into a problem with the Bolt 60 ...... it started blowing fuses when the standby is engaged. Anyone know why this would be happening?

[oc disorder]

I guess you mean "when the standby switch is switched to operate" i.e. from standby to on ...
First thing I would do is remove the 2 big power tubes , fit a new fuse , power it via a light bulb limiter
then turn it on. It could just be faulty tubes.

[aimeovaldi]

I do not know what a light bulb limiter is.... I do have new tubes that could be installed. Thanks for the info.

[Jazz P Bass]

Lamp Limiter Circuit.

https://www.google.com/?gws_rd=ssl#q...imiter+circuit

The idea is to 'limit' the current that a failed circuit (or a good one) is able to draw from the mains.
By limiting the current, you avoid unnessesary damage to the amplifier.

A working amp will have a brightly lit lamp at turn on, until the filter capacitors charge up.
Then it will go dim.

A failed circuit will show itself by never dimming the lamp.