After a stupid mistake which blew the PIC, I finished today my version of the uTracer. A quick trace of an CX-226 RCA Radiotron can be seen below. This is an incredible digital tester. I need to test it properly and do some comparisons against my analogue tracer, but as everyone would expect,the digital tracer has superior capabilities in terms of data manipulation and representation.
Highly recommended. Ronald provides a sterling service and specially when I damaged the PIC and send me a replacement at no cost!
A great record shop in Edinburgh. Highly recommended. Came out with some Thelonious Monk LPs. Even brewdog house is 5 min away. Enjoyed a 14% ale so can’t get better than this!
As discussed previously, I replaced the gyrator’s polypropylene caps with better ones I had at hand which are 1uF 450Vdc Mundorf Mcap EVO Silver Gold Oil Cap (EVOSGO-080). I should look at lower value. A 220nF or even 100nF one should provide a 1Hz -3dB point with the 4M7 resistor. Anyway, the sound is a tad better in the bass I would say. Nice upgrade but should listen to it more to find what other changes has this capacitor made to the amp:
Great thing about bank holiday weekends is that you have more time to work on your projects! At least I had this time round.
After doing the initial calibration to the Lenco idler mechanism, I got the turntable finally assembled on the new plinth. It runs very quiet and smoothly despite having not dampened the idler wheeler as recommended in the Lenco Heaven forum. I need to look into it but so far the turntable runs really quiet.
The arm board is a bit lower than it needs to probably. I can adjust the VTA with the micrometer but I should look at raising it to allow the arm to be rotated to the right for best placement. The micrometer is preventing this to happen. Will refine later.
GL75 now on its final place
Audiomods tonearm
First test
Clearaudio virtuoso cartridge
Ok, impressions so far after all this work then. I did many upgrades this time to my system so it is hard to quantify which part contributed the most to the sound improvement. Overall tone and clarity has improved. I suppose that the heavy plinth makes a big difference to the bass clarity. The overall tone improvement and detail is quite likely to be the Audiomods tone arm as well as using the Clearaudio Virtuoso Wood MM cartridge that Tony kindly give me to try.
A rare occasion in my hi-fi life is too see me switching from electronics to basic mechanics. I’m not either good with woodworking or mechanics :). Either way, the GL75 rebuild is coming along quite fast. I sealed the original arm holes in the top plate and painted it yesterday. Today, I spent all morning waxing the plinth. The afternoon was devoted to rebuilding the Lenco turntable mechanism and testing the re-lubed motor and spindle. I still need to do further calibration, but so far so good.
After owning several high quality pre-amps & modifying some of them to some degree or another, I decided to have a go at building a top quality unit, so here goes first I needed to build the power supplies for filaments & B+ in a separate case, I already had some idea of the look & design that I wanted to follow, so I sourced the following components from these suppliers:
One of the output 4-65a was actually a military JAN-8165. Wanted to test a pair of them but in the rush of building the amp I ended up with a mixed of the two. Not an orthodox approach buy who cares! After playing the amp extensively for a couple of weeks I noticed that this valve droped anode current after 1hour or more of playing. Anode current could go down by 10-15mA. Perhaps it has to do with the pin oxidation, but I also suspected on the filament regulator due to the heavy current required on this. The regulator heatsink gets really hot as you can imagine so I was already blaming on the regulator FET before I even suspected on this output valve.
A simple test was to replace this valve by a new NOS 4-65a. I did that and surprised to find that the filament regulator wasn’t to blame. The 4-65a SE filament stayed rock solid at 100mA after 1h30m of fantastic music. Yes, the bass of this SE is unique. It exceeded everything I previously listened to. Is the 46 driver in filament bias? Not sure yet, but hey ho. What an amp!
One of the problems I found when using the 4-65a SE amp was that my version of the Salas SSHV2 drifted significantly with temperature. This was due to the 01N100D characteristics (see extract from datasheet below). We can see that @ -1.5V VGS the temperature dependency is as much as 50mA/100°C. With the smaller heatsink I had before and the significant voltage drop given raw supply voltage levels this caused a problem:
IXYS IXTP01N100D datasheet extract
I then reduced the input raw voltage level to 300V to ease the power dissipation across this FET. This was not sufficient so I proceeded to look at various things on the regulator as described below:
Change log
Replaced M1 for DN2540. The DN2540 has a better temperature response. The voltage levels now allowed me safely use the DN2540 and no need for a 01N100D.
Added bigger heatsinks for M1 and M3. Even 2.5W across M1 would need a bigger heatsink if we are looking to run the CCS as high as 90mA.
Removed TP resistor to allow higher CCS current
Set CCS current to 85mA
Load will be now 30mA per channel (30mA each 46 driver valve)
Set output votage to 270V
Testing the SSHV2
All tested well in the workbench. I used an external CCS set at 60mA and the output voltage stabilisation was rock solid at 270V. Temperature of the heat-sink was around 40-45°C after 30min of continuous use.
Back in the 4-65a SE Amp, the raw supply level at full load was 297V. The regulator played nicelly at 270V and the CCS current drifted only 5mA from 90mA down to 85mA after 2 hours of continuous play. The temperature of the CCS increased only to 47°C whereas the shunt FET got up to 54°C given the continuous 7W dissipated on it. I may try to reduce the CCS current a tad to ease here.
The regulator is fitted back into the 4-65a SE amp
Played the amp for about 2 hours and slowly started to appreciate more and more the sweet sound of this beast. Bass has increased significantly in my systems and previously haven’t been able to extract the deep bass out of the SE amp through my Fostex FE167E full range drivers.
I’m really going to enjoy this amp for a while until I start looking at changes. Oh yes, many come to mind, but easy for now. Other projects are awaiting for a long time so far.
