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This afternoon, I found the wiring error that was not letting the Tone Circuits work in the Preamp. Selected the wrong 100k resistor on the bottom side of the Preamp Turret Board. After that, I have a quiet functional Hiwatt DR201 Bass Amp Clone/KT88/6550 Power Tube Test Fixture up and running. I let it run under burst pink noise drive feeding my Ampeg SVT115HLR Shop Test Cabinet for a while, listening to the tone circuits, watching the output at various levels of drive. Finally broke out my vintage Fender Precision Bass (eary 60's), and hammered away on that for a while.
I'm quite pleased with how this sounds as far as a working Bass Amp goes. THIS AMP KICKS ASS! One of these days, if that DR201 ever makes its' way down from San Francisco that I heard mention of after correcting a problem with the one that was here from Lon Cohen's facility nearby back in January, I'll get a chance to hear the differences. Not sure what we have on hand now over in our rental dept.
Having begun this project in mid-May of this year, this has been a steady sequence of challenges to first figure how I'd build this as a KT88/6550 Sorting/Batching test fixture, and then finally, having a pair of these discarded Blackstar S200 Guitar Amps that had been stage props, and found I had working power and output xfmrs, and very large/lopsided chassis to work with, this then took a turn to cobbling it into a Hiwatt DR201 Clone for a working amp to serve as the test bed for working with those big power tubes. All the day-to-day details are listed under the KT88/6550 Text Fixture thread. Final success with that Tone Circuit problem, this now feels like it has been a very worthwhile project. I still have more tasks ahead, but sure makes it nice to have what I was hoping for up and running with (thus far) no major issues.
The Blackstar amp has this large Power Supply PCB assembly inside that was set up for a variable power output stage to run the amp anywhere from 20W to 200W. I never did try and power it up, not having any of their service documents, and it didn't have all of the PCB's present, so I've hacked that board up to use it for brute force supplies. I may still change from the separate HT Screen Supply that I built using a salvaged Fender Hot Rod Deluxe Power Xfmr that had a failed thermal fuse open. Made simple aluminum mounting feet for it, and tucked it's heater and bias/bipolar supply windings inside the large end bell, with just the HT secondary winding exiting. And, there was NO AC heater winding in the Hiwatt Power Xfmr. So I added a 10A Heater xfmr to the package. It was already lopsided as far as the distributed weight goes, but now, that's far past what that silly single handle on top of their Cabinet was put on for a carry handle!
I was looking for around 700VDC and 400VDC for the HT Plate and HT Screen supplies. This is presently running around 710VDC and 375VDC. I can still adjust the HT Screen Supply upwards to get back to 400VDC, but, I also have the option of using the Center Tap of the P/T's HT winding to create a 350VDC Screen Supply. We'll see. That would remove a huge amount of heat that's being burnt up regulating the" too-high Fender HT supply" that I ended up with as a free P/T.
Next major task is tackling the cabinet. As I have a 120mm cooling fan to mount on the power tube end of the cabinet, I don't yet know what surprise I will envoke as I try to use a large dual-blade hole cutter to bore thru the lower side near the bottom/side wood joint. No doubt will encounter fasteners driven in to strengthen the joint that will object having a large diameter cutting tool trying to slice thru that end of the cabinet. May have to do this with a router.....should be exciting if there's sparks to be made with hidden fasteners underneath the Tolex. I have a sharp compass that can slice thru the Tolex, and then remove that from the covering before using the hole cutter.
Onward...........
I'm quite pleased with how this sounds as far as a working Bass Amp goes. THIS AMP KICKS ASS! One of these days, if that DR201 ever makes its' way down from San Francisco that I heard mention of after correcting a problem with the one that was here from Lon Cohen's facility nearby back in January, I'll get a chance to hear the differences. Not sure what we have on hand now over in our rental dept.
Having begun this project in mid-May of this year, this has been a steady sequence of challenges to first figure how I'd build this as a KT88/6550 Sorting/Batching test fixture, and then finally, having a pair of these discarded Blackstar S200 Guitar Amps that had been stage props, and found I had working power and output xfmrs, and very large/lopsided chassis to work with, this then took a turn to cobbling it into a Hiwatt DR201 Clone for a working amp to serve as the test bed for working with those big power tubes. All the day-to-day details are listed under the KT88/6550 Text Fixture thread. Final success with that Tone Circuit problem, this now feels like it has been a very worthwhile project. I still have more tasks ahead, but sure makes it nice to have what I was hoping for up and running with (thus far) no major issues.
The Blackstar amp has this large Power Supply PCB assembly inside that was set up for a variable power output stage to run the amp anywhere from 20W to 200W. I never did try and power it up, not having any of their service documents, and it didn't have all of the PCB's present, so I've hacked that board up to use it for brute force supplies. I may still change from the separate HT Screen Supply that I built using a salvaged Fender Hot Rod Deluxe Power Xfmr that had a failed thermal fuse open. Made simple aluminum mounting feet for it, and tucked it's heater and bias/bipolar supply windings inside the large end bell, with just the HT secondary winding exiting. And, there was NO AC heater winding in the Hiwatt Power Xfmr. So I added a 10A Heater xfmr to the package. It was already lopsided as far as the distributed weight goes, but now, that's far past what that silly single handle on top of their Cabinet was put on for a carry handle!
I was looking for around 700VDC and 400VDC for the HT Plate and HT Screen supplies. This is presently running around 710VDC and 375VDC. I can still adjust the HT Screen Supply upwards to get back to 400VDC, but, I also have the option of using the Center Tap of the P/T's HT winding to create a 350VDC Screen Supply. We'll see. That would remove a huge amount of heat that's being burnt up regulating the" too-high Fender HT supply" that I ended up with as a free P/T.
Next major task is tackling the cabinet. As I have a 120mm cooling fan to mount on the power tube end of the cabinet, I don't yet know what surprise I will envoke as I try to use a large dual-blade hole cutter to bore thru the lower side near the bottom/side wood joint. No doubt will encounter fasteners driven in to strengthen the joint that will object having a large diameter cutting tool trying to slice thru that end of the cabinet. May have to do this with a router.....should be exciting if there's sparks to be made with hidden fasteners underneath the Tolex. I have a sharp compass that can slice thru the Tolex, and then remove that from the covering before using the hole cutter.
Onward...........
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