Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems.

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Default Hartke HA3500 amp, tube v solid-state

The owner cannot detect a difference. Other than different gain settings
are obvious, how to set up and test? . I've not put a scope on there
yet, but what set of parameters to confirm there is a difference,
compressor or no compressor, max or min of contour settings, what sort
of level and frequency of presumably over-driven input? Test not
requiring guitar input and ear-drums, as then it becomes
subjective/musical ears required.
The valve actively tests fine.

Incidently seriously crap "engineering" on the speaker outlet board,
especially as it is PbF. 2 legged 1/4 inch socket, no extra dummy legs
for mechanical strength, so 2 simple active PbF joints supposed to hold
the pcb and 2 thick unconstrained supply wires , laughable.
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Default Hartke HA3500 amp, tube v solid-state



"N_Cook" wrote in message ...

The owner cannot detect a difference. Other than different gain settings
are obvious, how to set up and test? . I've not put a scope on there
yet, but what set of parameters to confirm there is a difference,
compressor or no compressor, max or min of contour settings, what sort
of level and frequency of presumably over-driven input? Test not
requiring guitar input and ear-drums, as then it becomes
subjective/musical ears required.
The valve actively tests fine.

Incidently seriously crap "engineering" on the speaker outlet board,
especially as it is PbF. 2 legged 1/4 inch socket, no extra dummy legs
for mechanical strength, so 2 simple active PbF joints supposed to hold
the pcb and 2 thick unconstrained supply wires , laughable.





There is a lot of audible difference between the valve stage and the
transistor stage in the HA3500, it's deliberately designed in.
If the owner can't hear this there is no point in him owning such an amp.


As for "testing" this stage, I would have to ask why do you need to test
this stage?
What do you hope to achieve by doing so?
How are your results actually going to make any sense?



Sometimes there is just no substitute for a pair of ears and a brain.




Gareth.


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Default Hartke HA3500 amp, tube v solid-state

On 03/12/2015 19:41, Gareth Magennis wrote:


"N_Cook" wrote in message ...

The owner cannot detect a difference. Other than different gain settings
are obvious, how to set up and test? . I've not put a scope on there
yet, but what set of parameters to confirm there is a difference,
compressor or no compressor, max or min of contour settings, what sort
of level and frequency of presumably over-driven input? Test not
requiring guitar input and ear-drums, as then it becomes
subjective/musical ears required.
The valve actively tests fine.

Incidently seriously crap "engineering" on the speaker outlet board,
especially as it is PbF. 2 legged 1/4 inch socket, no extra dummy legs
for mechanical strength, so 2 simple active PbF joints supposed to hold
the pcb and 2 thick unconstrained supply wires , laughable.





There is a lot of audible difference between the valve stage and the
transistor stage in the HA3500, it's deliberately designed in.
If the owner can't hear this there is no point in him owning such an amp.


As for "testing" this stage, I would have to ask why do you need to
test this stage?
What do you hope to achieve by doing so?
How are your results actually going to make any sense?



Sometimes there is just no substitute for a pair of ears and a brain.




Gareth.



So how does he or I determine whether things are as they should be or
that there is some failure with one or both of those channels?
I'll put a scope on there and suck it and see with different sine f and
levels of input and different other control settings.
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Default Hartke HA3500 amp, tube v solid-state

This is an ebay purchase. Forgot to say I pulled the valve and that
fully killed throughput of the tube channel. Reasonable looking DC on
the valve base. No provision in the schematic for adjusting bias , other
than component change in the self-biasing chain.
Another engineering problem with this amp. Steel cab bolts into tapped
alumimium and seized threads (whetever that steel/Al semi-welding
process is, not corrossion, melding?) . Previous person had ended up
sheering one of the bolts and stripping the heads of the remaining ones.
Matter of removing the corner protectors off the cab , then remove the
other bolts to the angle plates, then mole-grips on the sheered bolt stem.
Vaseline on all such threads before returning, including the replacement
4 x 6mm replacement front retaining bolts.
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Default Hartke HA3500 amp, tube v solid-state

Monitoring send out.
All controls mid, except graphic out, solid tate 0, tube mid and
compressor off.
Minimum sine input to show soft clipping is at about 400Hz, requiring
1.05V rms in. Then hard clipping coming in about 1.5V rms.
I'll take that as normal "tube" function


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Default Hartke HA3500 amp, tube v solid-state

On Friday, December 4, 2015 at 12:51:11 PM UTC, N_Cook wrote:
Monitoring send out.
All controls mid, except graphic out, solid tate 0, tube mid and
compressor off.
Minimum sine input to show soft clipping is at about 400Hz, requiring
1.05V rms in. Then hard clipping coming in about 1.5V rms.
I'll take that as normal "tube" function




Few bass players will drive this amp into clipping the tube.
The tube circuit has a very different EQ to the transistor circuit, which I would guess is pretty much flat.


Cheers,


Gareth.
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