ROLAND BOLT 30- 60 cycle hum...

[oc disorder]

Question, so this wire doesnt absolutely need to go to the fuse? It seems that the shortest path from the transformer to the board would be a good idea?

Could you move the fuses ? Or change them for another type if you get a serious problem it may save the transformer which would be a pain to replace.

Yes undo all the wires. That's called lead dress well how you arrange them. Try and keep power wires away from audio. You may have to lengthen some.

Maybe even a new power switch on the back leaving the old one for show you could try moving that.

Wires twisted like your heater/filament wires radiate less

EDIT: Try a large cap 1000uF 2200uF on those terminals again now its slightly less 4 & 5 on pre-amp board from memory
anything above 50v ....then try some small values ceramic or green cap also 50v or more .01 .1.

[czech-one-2]

Ok, got it apart again and it seems the purple wire from the main in jack to terminal #7 of the preamp tube board is also buzz inducing. Going to re-route it away from the wire loom...

[czech-one-2]

Yes! That purple wire was the noisy bugger. I routed it under the power supply board and there is zero buzz!
Put the original reverb unit back in just to keep it original.

[oc disorder]

A fine example of bad lead dress then. I'll remember this one !

[oc disorder]

Now for the mod !
As it stands the standby switch only cuts the HT from the centre tap of the output transformer
and thus the anodes but the screens are still connected which can lead to tube damage.

This modification cuts the HT to everything after the first filter capacitor.

If you don't want to cut the track you may have to mount a tag strip close by.

Use a sharp firm knife to cut the copper (not your fingers) twice , close together
and then your hot iron will help lift the tracks this time on purpose.
It's funny how usually it's bonded really well when you want to remove it
and then it falls apart when you don't!

You will probably have to lengthen the wire from the transformer and add one from the standby switch.
Double insulate the joins with two lots of heat shrink.

I better sign off

[oc disorder]

Here's a rough diagram showing the audio paths re is distortion channel and green clean. With the switch is either one or the other.

The standby switch is in its new position. 780k

[czech-one-2]

Thanks OC! Just to be certain, which wire from the transformer is the center tap and which wire from the standby switch? I dont want to mess up now as the amp is totally silent and has a superb clean tone!
[ATTACH=CONFIG]30631[/ATTACH

[oc disorder]

Thanks OC! Just to be certain, which wire from the transformer is the center tap and which wire from the standby switch? I dont want to mess up now as the amp is totally silent and has a superb clean tone!

Output transformer ct.. follow the wires back on the chassis and on the schematic.

From memory the O/P transformer CT runs back to the standby sw and the other wire from the
standby switch runs back to the point where we now want to put that wire from the transformer Terminal 7.

*** somehow terminal 7 label is missing from the Bolt 30 schematic at the power supply.
Its the one funnily enough directly above terminal 8!

You will have to trace it back and waste a few more cable ties.

My diagram "bolt 30 Standby Switch cct & brd" shows where it goes .. I would probably unsolder the brown wire from the transformer
and run it back to where D4 D3 and C1 meet having made the cut in the board to isolate that piece of track.
These standby switch wires I also would run on the other side of the power transformer near the chassis end if they will reach.
Then I would run a fresh piece of wire from that new pcb island where Terminal 7 (s/b s/w) and R3 meet back to the centre tap
of the output transformer where the old brown wire was (which we have now stolen for the new supply for the s/b switch).

Unless you replaced those 5w wire wound resistors I would guess a previous owner had a problem with the HT. tubes and screen resistors as on the diagram R3 560 Ω is a 2 watt resistor and the two screen resistors 470 Ω are shown as only half watt .
When these were replaced maybe that's when the lead dress got mucked up.

[oc disorder]

And to satisfy my curiosity could you now remeasure those test points for AC ?

It seems that may have been our biggest clue!

From your post #24
Ok, here's the reading:
TP 15V = 13.4v / 29.2v AC
TP 7.5v = 6.7v / 14.3v AC
48volt supply/R59 = 47.3V and 44V


post #26
The amp has been warming up for 30 min or so and using ground pad #5 on the preamp board here are my new readings
R58 44.6 / 40.6 DC , 12.5 / 12.5V ac
R59 45v /48v DC , 12.5 / 12.5 AC

then post #27
OK, little confusing,
Now I'm Getting
R58 98v / 89v AC and R59 98v / 105v AC

and your post #24
Just tried it with a neighbors meter, r58 = 98/89v AC and R59 = 98/105v AC

I'm just wondering what your meter measures now on the AC scale.

[czech-one-2]

Well, the chassis is happily back in the cab, but at some point I'll tackle the standby mod and at that time will post back those AC readings. Thanks OC for sharing your wealth of info freely here!

[oc disorder]

Ok, got it apart again and it seems the purple wire from the main in jack to terminal #7 of the preamp tube board is also buzz inducing. Going to re-route it away from the wire loom...

Well that's the input to the phase inverter (PI) on pin 7. Its really more like a line level input (cd player - tape deck - etc) so not as sensitive as a guitar or mic input
but it was acting like an antenna picking up "stray fields" radiating from the ac supply wires.
Replacing that wire with a piece of shielded cable would further reduce any possibility of noise getting in there.

I would only ground one end of the braid/shield probably at the jack and cover over any stray strands at the PI end with a neat piece of heatshrink.

Anyhow glad it all worked out in the end.. sometimes it ends up being the simplest of things.

If you ever come to Prague look me up and I'll show you around and treat you to some of the finest pivo [beer] on the planet!

Well thanks, If I'm ever in Prague I'll look for a muso using a bolt 30 and take you up on it !

[Bolt60]

Now for the mod !
As it stands the standby switch only cuts the HT from the centre tap of the output transformer
and thus the anodes but the screens are still connected which can lead to tube damage.

This modification cuts the HT to everything after the first filter capacitor.

If you don't want to cut the track you may have to mount a tag strip close by.

Use a sharp firm knife to cut the copper (not your fingers) twice , close together
and then your hot iron will help lift the tracks this time on purpose.
It's funny how usually it's bonded really well when you want to remove it
and then it falls apart when you don't!

You will probably have to lengthen the wire from the transformer and add one from the standby switch.
Double insulate the joins with two lots of heat shrink.

I better sign off

Hi and thanks all for such great informations !
i'm checking a Bolt 60 and would like to alert (if it's needed for other people as me)
that your standby switch board mod schematics is ONLY for Bolt 30 !

as on Bolt 60 there is R1 resistance so the wiring has to be changed here is mine



please let me know if you find a problem.

I'm looking for adjustable bias mod and did not find something usable to me (Roland Bolt 60 pdf is not detailed about it)
may someone know where to find proven Bolt 60 adjustable bias mod to start with ?

thanks,
have an happy new year
Phil

[Jazz P Bass]

I dug around that link that you posted & found this pdf. file.
The bias resistor is circled but there is no indication of what to do.
I would change the 6.8K resistor to 5.8K & add a 1K pot before it.

[Bolt60]

i have seen that resistor on the mod list but without info on what adjustable value to use and where to put it i'm still hesitant...

thanks for 1k pot value (seems low bandwith adjustment, it's enough ?)
i suppose i have to wire it on the 5,8K to ground side ?

I finished the standby switch mod,
i cut the trace between C1 R3 and R1
i cut the brown wire from CT transformer and wired it to pin 7 with red wire from standby switch
i made a hole and soldered the switch side of the brown wire to C1 R1 common et voilą



Though the way Standby switch work does not sound logical to me, when standby is to ON position so there is power flowing to CT,
if OFF there is no power to CT
Does this seems right to you ? i'm ignorant about using such Tube amp (it's for a friend who just purchased it) and this seems inverted to me
(should i just turn 180degre the switch on the panel board ?)

thanks for your advise,
Phil

[g1]

The wording used at standby switches is often poor. Better labelling would be standby/run or standby/operate. Usually when standby is labelled off/on, the "on" is operate position, "off" is standby mode. Yes, I agree it seems inverted, but that is how it is usually labelled.
For the bias JazzP mentioned, I believe he meant a 5.8K resistor in series with a 1K pot would replace the 6.8K resistor. This would allow you to increase the idle current of the tubes, but not decrease it.
The points shown as #10 in the mod list are where you would insert series 1ohm 1watt resistors between the power tube cathodes and ground. This would allow you to easily measure the idle current of the tubes when adjusting bias.