I bet they work fine with no heatsink.... Calculate the wattage requirement. What is the voltage differential across the 500 ohms? I bet there is only a couple of watts there. Or maybe I am wrong
BobW wrote:
Has anyone tried the little 500 Ohm 10W power resistors with aluminum casing? they are so tiny compared to the cement ones that is hard to believe they can withstand 10 watts. I just bought one but haven't tried it yet since I want to hear any comments on it. The size does make it atractive though, it will fit anywhere.
Be careful! The Al casing (DALE types, etc) dissipation ratings are based on a suitable heatsink, check the datasheet. A 12" x 12" x 1/4" heatsink plate is the usual standard heatsink reference. Try to mount it directly to the chassis and it should work fine.
I haven't actually tried the resistor/inductor swap out, and don't know the voltage drop/pwr dissipation. Based on past circuits, drawing about 1/2 the rating w/o a heatsink is usually enough to fry (in time) a Dale RH10 series.
So, assuming best case this resistor could take up to 5W =>
Max current = SQRT(5/500) = 100mA.
Assuming the resistor is at 5W dissipation => the voltage drop across the resistor is = 100mA * 500 Ohms = 50 Volts.
I doubt there is that much of a voltage drop across the resistor, so I have to agree with you, and think the resistor WILL be OK w/o a heatsink.
Thanks Dog for making me think this one out, sorry about the math.
Do you like the overall tone of the resistor vs the inductor?
Wow that's awesome Normster. I've built a spitfire and dc-30 but always wondered what a dumble type amp sounds like. Think I might build one.
Would it be better (for economy & newbies sake) maybe to have another input jack for the od channel and channel change with a/b box ala dc-30?
daz wrote:Wow that's awesome Normster. I've built a spitfire and dc-30 but always wondered what a dumble type amp sounds like. Think I might build one.
Would it be better (for economy & newbies sake) maybe to have another input jack for the od channel and channel change with a/b box ala dc-30?
That's an interesting idea, but it might be harder to implement than the OD switch. The ODS isn't really a two channel amp, it just uses cascading gain stages. The Clean channel sends the first two stages to the PI and the OD adds two additional gain stages between the Clean channel and the PI. To add foot switching to this design, just use a relay in place of the OD switch. I may build a "Lite, Stage 2" with OD footswitch for those ready to take it to the next level. It's pretty easy, especially if you have an unused 5V tap on your PT.
When using the Bassman OT on this type of amp with 6V6's, do you guys adjust the speaker load to reflect it back onto the primary impedance of the OT?
I believe the Bassman OT has a 4K primary and 4 secondary. Can some confirm? It would be nice to have a multi-tap Bassman OT.
fp2000 wrote:When using the Bassman OT on this type of amp with 6V6's, do you guys adjust the speaker load to reflect it back onto the primary impedance of the OT?
I believe the Bassman OT has a 4K primary and 4 secondary. Can some confirm? It would be nice to have a multi-tap Bassman OT.
If you have a Bassman OT, I'd just run 6L6's. The only reason I went with 6V6's in this build was to save money on iron. Based on my VERY limited understanding of OPT and NFB, it appears that Dumble uses -8dB feedback to the PI. (I may have mis-applied some of Randall Aiken's formulas so all of you EE's please feel free to correct me.) I think Gil said that the only 50watt Dumble he's ever seen had 8k/1k NFB resistors.
Normster wrote: As for the radial caps, that's a good idea. They can easily be mounted with the leads through the board and bent over to an eyelet.
You can also sideways mount radials, A dab of silicone secures them.
At least that way they can be removed from the top.
I say do the full kit, relays arent hard if maybe you supplied a daughter board for them. IF someone cant handle the relays they shouldnt be building an amp
Luthierwnc wrote:One thing that has helped me out over the years is doing an Excel spreadsheet for parts. If I have a couple amps going, I run columns for; part, part number, quantity, vendor, price and then which build it is for. No matter what sequence you enter items, you can resort by vendor, cut and paste and have your BOM. It works especially well for Mouser since you can download it directly to their order sheet.
sh
If you use Designworks or Eagle for Schematic you can put all that info attached to the part, then you generate a parts list, create a hyperlink in excel and it takes you right to the part at their website, click the next part and it adds that, it is really cool and effortless
