Tube Amps / Music Electronics
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|9/18/2000 4:16 AM|
||Re: SLO-100 Clone - To PCB or not...|
Mitch and Joe,
After studying the pics Dave provided, I am certain that the SLO uses a separate PT tap to feed the LDR supply. You can see a white twisted pair lead which originates from the grommet of the PT, runs under the main board, and apparently (can't see for sure, but there are no other connect points for this) to the bridge recto for the LDR circuit. This may be a 5V tap.
I also modeled moving the 61.9 ohm resistor before the 33 ohm resistor in the LDR circuit in ER Studio, and it seems to work well and make sense.
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|9/18/2000 1:35 PM|
I see that also Jeff. It does show it that way on the schematic we have and I've never questioned that fact. It is so much easier to deal with than trying to rectify and isolate the filament supply to do double duty.
Hmmm, probably not. When I model it in Electronics Workbench, it needs 6.3vac or higher to really turn on the LDRs. Remember, this is a custom PT and they can get any voltage they want. What is the program you tried to model it in? ER Studio? What is that?
The values looked very balanced across the LDRs when I modeled it also. But my incorrect version works fine! I get about 1.62 volts across the LDRs in either mode in the operating circuit. I wonder if that is not too high and is the reason I've toasted two LDRs before?
|9/18/2000 3:42 PM|
>>What is the program you tried to model it in? ER >>Studio? What is that?
I meant Electronics Workbench, sorry for the confusion.
I just modeled it again, and you are correct, the 5V is not enough to fully turn on the LDR's. It's probably right about 6.3 - 6.5 V.
Looks like I may have to do a separate transformer for that.
Looks like the LDR's don't like currents above 40mA, but you should be well under that. It does seem to work well with that resistor moved though.
|9/18/2000 7:25 PM|
This question isn't really soldano specific but relates to the topic... I've got a seperate 6.3 vac (more like 6.8 under no/small load) transformer that I was going to try for the LDRs in my X88R/SLO head but I want to to keep the negative side of the supply grounded (to avoid having to isolate the chassis jacks etc.). This particular transformer is not center tapped, I really don't know much electronics at all (other than how to clone an amp!), and I've got no idea how I could get 6.3 +/- VDC off of this thing AND keep the negative side to ground. Is this even possible?
Help is always appreciated
|9/18/2000 8:16 PM|
If I understand the question correctly, you would use a bridge rectifier. Actually this is basically what Soldano does in their amp, but instead of a separate transformer, they use a sperarate non center tapped winding and then using a integrated bridge rectifier.
|9/21/2000 4:32 PM|
Where can you get the ldr's used in the slo? I found one place on the net but was just wondering if any major suppliers like mouser etc. had them. Are they the same as any four pin optoisolator just they happen to work well cause they are easier to work w/ than an 4 pin dip package? The schematics show them differently and i tried to find data sheets on the ones used in the slo but couldn't find any info. Thanks. Tim
|9/21/2000 8:19 PM|
The absolute cheapest place to get them is from Allied Electronics. They are less than $4 each, and I'll bet you saw them for around $10 elsewhere.
Their site is: http://www.alliedelec.com/
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