Diagnosis:  When we open up, we notice almost everything (over hundred of parts and bits!) are being replaced. Some areas have increase numerous fold of values for safe guard, some important locations with false direction / polarity, some hair splitting wirings and solders, some fine bits...etc. Of course all of the above would not help the cause for the hum and distortions.

Solution: With almost the whole circuitry being messed up with. We decide to scrap it and install like the original. Like all amps we work on. We provide thorough testing, not only limited to real world driving and listening tests. We provide alignments often on several sections, balancing and matching parts and outputs, as well seeing the report card (measurements) as good or better than factory. We deal with real causes, not patching jobs.

Diagnosis:  After our diagnoses, we have found more problems than mis-used. Just look those original charred and near blowing up caps.

Solution: A bit of a work has to be done to fix it up. But at the end, we did not just bring it up to working mode, but surpassed its original spec and sound with better parts and components at all spots where we think it is worth / should be changed. This tube pre should have decades of reliable operations.

More interesting question marks follows...

Diagnosis:  So after we examine the circuitry. We believe the silkscreen printing / labels on the amp is out of date, and in correct. The amp should run with 6922 / 6DJ8, not 12AT7 nor 6P1. The tubes went bad anyway. As per customer request, we have relabeled the amp. Now, to the flipping switch from the NORMAL PENTODE to nowhere land (somewhere not normal perhaps).

It actually takes you to Triode mode, instead of UL, but the output transformers impedance is really / better for Pentode. And looking at the DC supply stage, it is a low cost design which save an additional power choke for DC filtering. This is what stirring up the noise in triode mode. Which is as it, if you want to listening in this side of the switch. Even you can live with the noise, we don't understand why add the switch if it isn't meant for triode. Its just a switch for trouble in long term, well this case not that long.

Solution: The whole scenario only requires simple components and circuitry upgrade, of course with better ones, along with new tubes. After bench test completed, everything checked normal; The noise and distortion are actually not bad, when running in the "normal" Pentode mode of course.

Diagnosis:  After thoroughly inspections, we found both channel have hi distortion outputs as nominal power output. Channel output is also unbalance and have hum noise, as well kicking noise.

Solution: Remove defective parts and replace with better parts, as well do a recap and change all signal path resistors. Provide burn in test and electric bench test for (running checks), ensuring a stable performance and low distortion for rated power output.

Diagnosis: Standard procedures...

Solution: Overhaul we go...

Diagnosis: Standard procedures... and this is one of the best Pioneer we have seen, as well best kept original, all tubes are original Hitachi, heard the unit has been sitting in closet for all its life. Only few things needed to change.

Great quality example from Japan from the 60s, nothing is made like that today and sound like that again. I have encountered and fixed one of these back in my high school days - see my picture of my textbook.

Solution: To the rescue...

Diagnosis: Several bad contacts, failed transistors, and bad solders.

Solution: Took us quite sometime in looking for direct replacement of these old transistors... But not a problem! I was their (Accuphase) factory trained technicians back in the old days for the import firm... including several other major Japanese brand name.

Diagnosis: He definitely came to the right place!

Solution: Everything new installed including the transformer...we even have a new PCB for this. The spec is FAR better than original.

Diagnosis: Follow instructions and replaced provided parts.

Solution: If you also have a Fisher tuner/receiver, bring it to us! We have the parts ready to do the same set of overhaul suggested by the restore guide.

Diagnosis:

Solution: Our typical gone over...

We did a ground up redesign for this power hungry customer, using minimal of the old parts (old transformer/part of the PCB), redesigning our own version of 200 watt Hybrid power amp. Although we are tube specialist, but we started out and were professional solid state circuitry engineer/designer.

Diagnosis: Strip out everything, and install our new design, including our own PCB and all these new parts & components. Sourcing the transistors from Japan took us the most time... but the reward is certainly worth the wait!

Solution: This project took us weeks to complete and it isn't cheap, but this is a good example of what we can do for our portfolio. Looking forward to design more hybrids for our OEM customers.