what frequency?
there is a natural drift at around 60 and 120.
there is a natural drift at around 60 and 120.
HP 200CD
- Thread starter CJ
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Help Support GroupDIY Audio Forum:
This was at around 1kHz. It has done this occasionally all the time I have had it, but now it's constant. When you watch the waveform on the scope the voltage fluctuates quite a lot - more than it has done until now.
Best regards,
Mikkel C. Simonsen
Best regards,
Mikkel C. Simonsen
try swapping the small tubes, not the output tubes,
I'll try locating a pair of 6AU6s in my junk pile...
I found a voltage chart in the manual, and the voltages seem to be "skewed". The positive supply voltage should be 225V according to one page and 215V according to another. It's only about 200V. The negative should be -155V, but it's about -175V. So the total (380V +/-75V) is correct, but the individual voltages are off. The absolute voltages on the output tubes are also off, but there's still 16V of bias etc. Perhaps I should have a look at the carbon resistors also...
Best regards,
Mikkel C. Simonsen
I found a voltage chart in the manual, and the voltages seem to be "skewed". The positive supply voltage should be 225V according to one page and 215V according to another. It's only about 200V. The negative should be -155V, but it's about -175V. So the total (380V +/-75V) is correct, but the individual voltages are off. The absolute voltages on the output tubes are also off, but there's still 16V of bias etc. Perhaps I should have a look at the carbon resistors also...
Best regards,
Mikkel C. Simonsen
I found a new set of 6AU6WCs, but they didn't make any difference. I have had a look at the resistors also, but nothing looks strange (it's hard to measure accurately when everything seems to be DC-coupled...). I have also checked that the light bulbs work and I had a look at the ripple on the supply voltages - everything looks fine. But it still doesn't work 
Best regards,
Mikkel C. Simonsen
Best regards,
Mikkel C. Simonsen
that leave the capacitors,
leaky filter caps will skew your pwr supply voltages a bit, although 10 to 20 percent is normal for tubes,
leaky caps in the osc circuit could also be a problem, i would swap them out first.
kind of a job, they are tucked into the middle of the chassis.
leaky filter caps will skew your pwr supply voltages a bit, although 10 to 20 percent is normal for tubes,
leaky caps in the osc circuit could also be a problem, i would swap them out first.
kind of a job, they are tucked into the middle of the chassis.
CJ said:
Most of the amp/oscillator circuit is on a small board in mine (the '65 version). With some difficulty I got it out, and I replaced the two coupling caps. I replaced the resistors also, now that the board was out... That didn't help though. I replaced some of the mica caps also - they apparently cause problems in these oscillators sometimes. But still no luck. I thought the problem was fixed initially, as the output voltage was lower and stable. But after switching the power on and off six or seven times the problem came back. The output voltage is again too high (I can't set it at 12V as you're supposed to), and the voltage jitters up and down a bit. The wild tremolo seems to have gone, but the voltage is still unstable... The only cap left is the 100µF 100V bipolar. Can you even get such a beast anywhere?
Best regards,
Mikkel C. Simonsen
yes that cap is a pain, i used a couple of 200 uf, back to back,
make sure the light bulb connections are good, that is a real low resistance circuit they have there,
any small resistance change in that area can throw things off, you can solder the rivets on the sockets,
make sure the light bulb connections are good, that is a real low resistance circuit they have there,
any small resistance change in that area can throw things off, you can solder the rivets on the sockets,
CJ said:
Yes, I noticed that potential problem, so I soldered the lamp sockets. It looks like one of the problems in mine was the output level trimmer. Getting it out of the PCB was a bit difficult, so I added a fixed level "trimmer" using two resistors. Now the level looks stable, and I hope it stays that way...
The distortion at 1kHz is about 0.06% now. I guess that's OK with the manual spec being 0.2%
Here's a photo of the guts of the PCB version of the 200CD.
Best regards,
Mikkel C. Simonsen
My pair of 200cd's are out for delivery today , fingers crossed its all safe and sound .
I saw 100 GE black plate 6au6's for auction on ebay , ended up getting them for 40 euros ,plus 15.99 shipping from Germany .
I should be able to select nicely matched pairs from that lot , as far as I can tell both units Im getting are late model ,one Alto,Usa one West German made ,6AU6 and EL86.
I found an interesting thing in one of the manuals online , where part of the spec requirement is to change models with the silicon rectifier back to tube rectified ,complete with new mains transformer providing 5 volt heater supply .
http://www.hparchive.com/Manuals/HP-200CD-Manual-SNP_605.PDF
the last page of this documents the change back to tube rectification , then they have you verify the % distortion on the output of the gen
I saw 100 GE black plate 6au6's for auction on ebay , ended up getting them for 40 euros ,plus 15.99 shipping from Germany .
I should be able to select nicely matched pairs from that lot , as far as I can tell both units Im getting are late model ,one Alto,Usa one West German made ,6AU6 and EL86.
I found an interesting thing in one of the manuals online , where part of the spec requirement is to change models with the silicon rectifier back to tube rectified ,complete with new mains transformer providing 5 volt heater supply .
http://www.hparchive.com/Manuals/HP-200CD-Manual-SNP_605.PDF
the last page of this documents the change back to tube rectification , then they have you verify the % distortion on the output of the gen
> documents the change back to tube rectification
They are not telling you to change-back to tube rectifier.
They made eight different sub-models. That manual covers the last model. Appendix C lists the changes so you can use the one manual to service any of the eight sub-models. If your machine is not a "333-" prefix, you will not find crystal rects, you will find a bottle; the difference is shown. ALSO, the "333-" prefix is rated 0.2%THD, the other seven sub-models were rated 0.5%THD. It is not clear that this is about the silly-state diodes; more likely by this time they had so much experience (and maybe a competing product) that they were comfortable with the lower number.
You are not expected to take a newer sub-model and "back-date" it to an older spec. In fact change #5 says R23 R24 used to be 820K; but in case of a specific problem, you can use the value in the latest change (1.5Meg)
They are not telling you to change-back to tube rectifier.
They made eight different sub-models. That manual covers the last model. Appendix C lists the changes so you can use the one manual to service any of the eight sub-models. If your machine is not a "333-" prefix, you will not find crystal rects, you will find a bottle; the difference is shown. ALSO, the "333-" prefix is rated 0.2%THD, the other seven sub-models were rated 0.5%THD. It is not clear that this is about the silly-state diodes; more likely by this time they had so much experience (and maybe a competing product) that they were comfortable with the lower number.
You are not expected to take a newer sub-model and "back-date" it to an older spec. In fact change #5 says R23 R24 used to be 820K; but in case of a specific problem, you can use the value in the latest change (1.5Meg)
H'Ooooops ;D
The guy only sent me out one unit , when the auction clearly shows its two units .
Had to email the seller and throw a spanner in the works ,anyway Im sure it will all be sorted out .
The one that arrived is in good nick ,power cable is perished beyond use,tuning mech in desperate need of lube , all tubes correct and present ,although the tube rectifier has been replaced by solid state ,and a couple of resistors in series ,the 5 volt winding is available if nessesary . The size and scale of it is bigger than I thought ,Its really beautifully made ,everything looks way overspec, transformers of that bulk wouldnt be out of place in a vintage 50 watt guitar amp .
From the literature I read the makers took great care to produce an instrument thats a joy to use ,front panel layout is especially nice ,I can easily see why this unit holds a special place for anyone who used one . The manual is also a masterpiece in its own right ,all the test procedures are clearly explained and very easy to work through . It also happens to be one of the main types of audio oscillator used in the very earliest days of electronic music ,there seems to be a slightly unique wonk to the sound when you change frequency ,in other words the settleing time .
I'll do some cold tests first then wire it up and have a look . its still got the dreaded pink caps in place and everything else besides the rectifier wiring looks original too .
So the tube rectified version achieves better performance ,by the looks , wouldnt anyone have sworn if anything silicon diodes would have been better ? so can a tube rectifier actually reduce the distortion in audio, is that what were seeing here ?
The guy only sent me out one unit , when the auction clearly shows its two units .
Had to email the seller and throw a spanner in the works ,anyway Im sure it will all be sorted out .
The one that arrived is in good nick ,power cable is perished beyond use,tuning mech in desperate need of lube , all tubes correct and present ,although the tube rectifier has been replaced by solid state ,and a couple of resistors in series ,the 5 volt winding is available if nessesary . The size and scale of it is bigger than I thought ,Its really beautifully made ,everything looks way overspec, transformers of that bulk wouldnt be out of place in a vintage 50 watt guitar amp .
From the literature I read the makers took great care to produce an instrument thats a joy to use ,front panel layout is especially nice ,I can easily see why this unit holds a special place for anyone who used one . The manual is also a masterpiece in its own right ,all the test procedures are clearly explained and very easy to work through . It also happens to be one of the main types of audio oscillator used in the very earliest days of electronic music ,there seems to be a slightly unique wonk to the sound when you change frequency ,in other words the settleing time .
I'll do some cold tests first then wire it up and have a look . its still got the dreaded pink caps in place and everything else besides the rectifier wiring looks original too .
So the tube rectified version achieves better performance ,by the looks , wouldnt anyone have sworn if anything silicon diodes would have been better ? so can a tube rectifier actually reduce the distortion in audio, is that what were seeing here ?
I used a HP200 on my bench back in the early 70s... good general purpose work horse.
JR
JR
After a few drops of light machine oil the dials turning a lot nicer , but the fine tune seems to slip a bit , the grub screws on the knobs are on very very tight and Im afraid Ill break or damage it if I apply to much force. I see theres a tension spring on the fine tune thats adjustable depending on how much you push the dial onto the shaft , maybe in time the fresh oil will loosen things up and it will work right .
Im being very carefull not to disturb anything as I clean ,as well as replacing the same valves in the same sockets , I'll do a quick run around the caps for leakage then see if it will power up .
Seller got back to say he intended to only make the listing for one unit ,but the page clearly states items 198+523 ,as well as showing pictures of both units ,and there was no option to buy more than one item on the buy it now either , Im holding tough
balls back in his court for now so we'll have to see what happens .
As the years of grease and grime have come off some of the extra attention to detail becomes visible , like the engraved nomenclature on the front panel/dial , I cleaned the paintwork on the case with soap and a fingernail brush , comes up like new save the odd dint n ding . Its a 103 prefix model this one .
Im being very carefull not to disturb anything as I clean ,as well as replacing the same valves in the same sockets , I'll do a quick run around the caps for leakage then see if it will power up .
Seller got back to say he intended to only make the listing for one unit ,but the page clearly states items 198+523 ,as well as showing pictures of both units ,and there was no option to buy more than one item on the buy it now either , Im holding tough
balls back in his court for now so we'll have to see what happens .
As the years of grease and grime have come off some of the extra attention to detail becomes visible , like the engraved nomenclature on the front panel/dial , I cleaned the paintwork on the case with soap and a fingernail brush , comes up like new save the odd dint n ding . Its a 103 prefix model this one .
Attachments
All the caps checked out good both in value and for leakage so I powered it up , nothing ,then a moment later a small click and it came on ,sure enough Ht came right up to about 320 before settling back to around 210 , next turn up the output ,yep its putting out signal too all going great 10-15 volts output then poof ,the fuse gently faded out , I had used a 250ma in place of the speced 600 ma , no surprises there , there was some corrosion around the fuse socket also,which explained the earlier intermittant contact . Im out of .6 amp fuses for now ,so nothing more I can do tonight , looks like my machine is good though .
I tried again this evening with a 630 ma fuse ,worked great for a while ,25 volts signal output , then one section of the electrolytic overheated and exuded some black nasty , I caught it early . For now I just wired out that cap section as its already in parralell with other sections , Ht volts is a bit low now but still works ok now again, Ill have to look at beefing up the psu caps in any case , I also dont understand the 40Uf with the 10K ohms in series .
Is hundreds of Uf ok for second and third smoothing cap ? to lower hum ,which is quite high now .
Is hundreds of Uf ok for second and third smoothing cap ? to lower hum ,which is quite high now .
