New builder with a couple questions

2nd harmonics for the masses

New builder with a couple questions

Postby katabatic » Wed Apr 07, 2010 11:15 am

Hi - Building the GSE will be my first new construction since assembling my Dyna FM-3 back in 1970 or so (though I recently recapped it and a Dyna SCA-80). In going over the schematic, parts list, and instructions I have a couple hopefully-not-too-stupid questions that I'm hoping someone can help me with:

1. Capacitors C3 and C4 are shown as 220uF on the schematic and parts list, but as 100uF on the circuit board diagram. I'm assuming 220uF, right?

2. On the schematic showing the connection of the terminal blocks to the 6B4g sockets, the left channel has terminal 5 going to pin 7, and terminal 4 to pin 2. The right channel has terminal 5 going to pin2, and terminal 4 to pin 7. Since it's the heater, is that ok, or should they match?

3. The assembly instructions talk about Rxx, a future bleeder. Is that R21?

4. Is it critical to use the recommended Nichicon caps for C5/C6 and C11/12/13/14 (Mouser is out of them), or can same-value/voltage electrolytics of another brand (like Xicon) be substituted?

That's it for now, although I'm sure I'll have more questions along the way. I'm still amassing parts and reading my RCA tube manual, and yes, I will try very hard not to electrocute myself! Thanks!

George
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Postby TomMcNally » Wed Apr 07, 2010 1:35 pm

Hi George - Welcome to diytube.

1. Capacitors C3 and C4 are shown as 220uF on the schematic and parts list, but as 100uF on the circuit board diagram. I'm assuming 220uF, right?

** Bigger is better !

2. On the schematic showing the connection of the terminal blocks to the 6B4g sockets, the left channel has terminal 5 going to pin 7, and terminal 4 to pin 2. The right channel has terminal 5 going to pin2, and terminal 4 to pin 7. Since it's the heater, is that ok, or should they match?

** I never noticed that (I only built about 8 of these!) it doesn't matter

3. The assembly instructions talk about Rxx, a future bleeder. Is that R21?

** Yes R-21 is the bleeder, it wasn't present on early boards

4. Is it critical to use the recommended Nichicon caps for C5/C6 and C11/12/13/14 (Mouser is out of them), or can same-value/voltage electrolytics of another brand (like Xicon) be substituted?

** Any caps are OK, just make sure the diameter and height will
fit on the board and under your chassis.

Tip: if you didn't solder any parts on the board yet, use the blank
board as a drilling template if you are making your own chassis
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Postby Ty_Bower » Wed Apr 07, 2010 3:06 pm

TomMcNally wrote:2. On the schematic showing the connection of the terminal blocks to the 6B4g sockets, the left channel has terminal 5 going to pin 7, and terminal 4 to pin 2. The right channel has terminal 5 going to pin2, and terminal 4 to pin 7. Since it's the heater, is that ok, or should they match?

** I never noticed that (I only built about 8 of these!) it doesn't matter


The reversal is not accidental. Some have expressed concern about using DC to heat filaments which are normally expected to be heated with AC. Due to the voltage drop along the length of the filament, one end is at a slightly different potential (6.3 volts) with respect to the other. The worry is that one side of the filament is going to "wear out" sooner than the other. The cure in this case is to periodically swap the power tubes, much like rotating tires on your car.

There's a thread around here somewhere that mentions this. If I find it, I'll post the link.

edit: I think this is the one:
http://www.diytube.com/phpBB2/viewtopic ... ight=#8127
"It's a different experience; the noise occlusion, crisp, clear sound, and defined powerful bass. Strong bass does not corrupt the higher frequencies, giving a very different overall feel of the sound, one that is, in my opinion, quite unique."
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Postby katabatic » Wed Apr 07, 2010 5:30 pm

Thanks, guys. This is definitely going to be a learning experience!
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Re: New builder with a couple questions

Postby Ty_Bower » Wed Apr 07, 2010 7:03 pm

katabatic wrote:4. Is it critical to use the recommended Nichicon caps for C5/C6 and C11/12/13/14 (Mouser is out of them), or can same-value/voltage electrolytics of another brand (like Xicon) be substituted?


I asked a similar question here...
http://www.diytube.com/phpBB2/viewtopic.php?t=3377

...and received a similar answer. I did end up ordering all parts as specified on the parts list (no back-orders). I think if you are willing to spend the time doing the research, you can find good (or even superior) substitutes. Just be sure to read the manufacturer's datasheets for each part under consideration - don't trust Mouser's specs to be accurate. 105 degree ratings are always better then 85 degree. Lower impedance is preferable to higher. Longer life seems like an improvement over shorter. Lead spacing is critical - it must match exactly. Component height can most likely tolerate some variance, assuming you've got a little depth to spare in your chassis. Diameter is another story, as some of these parts don't have a lot of extra space around them.

Here's another capacitor tip: When you solder them to the board, don't press the cap tight against the PCB. Let it fly a millimeter or so above the board. The parts will expand and contract as they heat and cool with the normal thermal cycles of the amp. If the cap is tight against the board, it'll pull slightly on the leads each time things shrink. This will shorten the useful life of the cap.
"It's a different experience; the noise occlusion, crisp, clear sound, and defined powerful bass. Strong bass does not corrupt the higher frequencies, giving a very different overall feel of the sound, one that is, in my opinion, quite unique."
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