burns orbit 2 tremolo issue

[Arbutt]

Hello
I'm having an issue with the tremolo on this one.
Quick story
It came in a few months ago for being really noisy after changing a ton of stuff it was silent and working well
( well so i thought)
about a few weeks after i received a call saying it working , but Channel 1 is a little over driven.
On testing i confirmed this and found channel 2 Good and tremolo working ( connected to channel 1 only)

Unfortunately there is no schematic for orbit , but have the 3 version

To be honest i started to play around with it and got channel 1 working and sounding as it should. Put the amp down for a bit didnt write any notes, now i can't remember what i did really

to cut a long story short the channel is now sounding great no overdriven sounds. But the tremolo is not working very well its hardly usable as present

As i didn't touch any of the tremolo circuit i'm thinking the fault has to be with 2nd stage transistor

the hand drawn picture is drawn from what i see on the amp now

If any of you guys can advise many thanks
have a nice weekend all

[Jazz P Bass]

The base emitter voltages do not look right to me on that final transistor.

[Helmholtz]

Vbe of Germanium transistors can be as low as - 0.1V.

[Arbutt]

thanks jazz p bass. this is the same component layout than on the orbit 3 diagram
what should they be more like. any ideas on what they should be
thanks again

[Helmholtz]

Ge transistors have a Vbe between 0.1V and 0.4V. Best measured directly between pins.

BTW, all voltages in the Burns schematic should be negative.

[Arbutt]

Ge transistors have a Vbe between 0.1V and 0.4V. Best measured directly between pins.

BTW, all voltages in the Burns schematic should be negative.

thanks Helmholtz do you see anything wrong with the circuit, amps sounds good when trem is one just weak
where can i start where would you start
many thanks
Arbutt

[Helmholtz]

The upper right transistor in your hand hand drawn schematic corresponds to TR17 in the Burns schematic and the lower right one to TR3. TR17 controls/modulates the supply voltage to TR3. Does the -10V collector voltage pulse with tremolo?
If not, check if the collector voltage of the LFO transistor TR16 (-16V?) is pulsing.

Also check if all (replaced) ecaps are installed with correct polarity, meaning opposite to positive supply amps.

[Arbutt]

The upper right transistor in your hand hand drawn schematic corresponds to TR17 in the Burns schematic and the lower right one to TR3. TR17 controls/modulates the supply voltage to TR3. Does the -10V collector voltage pulse with tremolo?
If not, check if the collector voltage of the LFO transistor TR16 (-16V?) is pulsing.

Also check if all (replaced) ecaps are installed with correct polarity, meaning opposite to positive supply amps.

Thanks Helmholtz
The tremolo circuit ( TR16/17 is working as it should and pulsing but it seems to have very little effect on TR3 in the way it should
when you engage the tremolo with the foot s/w and have all controls full on its there but weak,
when the amp came in the tremolo was working correctly and no work has been done to the tremolo circuit, only worked on 1st and 2nd stage transistors.

Any caps that have been changed are correct and fitted correctly ,
I will measure the voltages again later and put them up

[Helmholtz]

TR3 is part of the tremolo circuit. Changes to this stage will change the tremolo strength.
TR 17 modulates the voltage at the node R9, C6, R33. This is the supply voltage for TR3. Should be -15V.
TR3 gain depends on its supply voltage, more exactly on the voltage drop across its collector resistor R33 (should be around 5V).

Please see if the -15V is pulsing.

[Arbutt]

ok i have some better news, While i was playing with it, i found by just having the 4.7k and the 100uf from the emitter
has sorted the issue
I now have the tremolo back as it should. comparing the channel one to channel two ( Vol and treble) on the orbit 2
all sounds about the same

I want to make sure everything is now as it should so when i return it, i can safely say it at its best

-27v supply
-17v at C6
-11v in collector of second stage transistor ( TR3)
-1.4v on base
-1.3v on emitter
R33 is now 22k
R32 ? ( burred out ) 100k
R29 is 10k
Can you see anything wrong with above or any improvements ?

I think all i have to do now is tidy it up

[Helmholtz]

While i was playing with it, i found by just having the 4.7k and the 100uf from the emitter
has sorted the issue

Not clear what you did.

[Arbutt]

Not clear what you did.

sorry for the delay. I removed the 220R ( R30) so just have the 100uf and 4.7k connected from emitter to the ground
This has given me the tremolo back and working correctly

[Helmholtz]

Thanks for clarification.

Seems the new TR3 has less gain than the old one and you had to design it in.

If everything works now - congratulations!

[Arbutt]

Thanks for clarification.

Seems the new TR3 has less gain than the old one and you had to design it in.

If everything works now - congratulations!

Well not quite

I have all channels working along with a good tremolo and clean sounds . This channel has i think a little too much background hiss
If i removed the signal input to the power amp, No hiss all quite, If i leave channel 2 connected all quite
If i just have channel one connected i get a background hiss

I decided to replace 2nd stage transistor NKT213 for a new one. Just to be sure.
I'm 90% sure that its the 2nd stage transistor and i do remember the amp not having this hiss at the start
I have tried to see it on the scope, but i can't see the noise
I have checked lead address and fitted some screened cable
Isolating the 1st stage transistor from 2nd stage hiss still present

Tr3 ( 2nd stage) Collector
-15v supply and -9,5v at collector
-1.3v on base
-1.2v on emitter ( 4.7k and 100uf) to ground

First stage transistor
-22v supply and -4.6v at collector
-4.2v on base
-4.3v on emitter

Not sure what to do now any assistance is helpfull
Mr A

[Helmholtz]

sorry for the delay. I removed the 220R ( R30) so just have the 100uf and 4.7k connected from emitter to the ground
This has given me the tremolo back and working correctly

Your replacement transistors may just be more noisy than th original one.

But looking again at this extremely hard to read schematic, I think you cannot just omit the 220R resistor.
On one hand the TR3 stage will have more gain without the resistor (increasing noise) and OTOH the resistor is used to produce some signal at the TR3 emitter.

Reinstall the 220R and if necessary somewhat lower the value of R31.

And remember that Germanium devices are extremely heat sensitive. The can be easily damaged by heat during soldering. Don't cut the leads too short.