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Tube DIY Asylum Do It Yourself (DIY) paradise for tube and SET project builders. |
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Tube DIY Asylum Do It Yourself (DIY) paradise for tube and SET project builders. |
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In Reply to: Dissecting an Audion Sterling ETSE EL-34 integrated after a loud "Pop!" and smoke (pics & schematic included) posted by darkmoebius on April 27, 2006 at 22:42:53:
First off, I want to thank everyone for their helpful advice. I labeled all the leads, unsoldered everything and removed the signal board (more pics to follow). Check below for responses to individual posts.I should have mentioned at the start that I did not draw the schematic in my first post, it was emailed to me by someone last year. There are few minor resistor value differences between my amp and that schematic, most probably the result of trouble discerning marking color on the really small ones. Hell, I had to really squint to make out some of them.
Although, the Power supply resistors are significantly different - 422k in his and 681k in my amp. Also, the PS resistor between the two final 220uf/250V caps going to the 1st & 2nd stage(15k his, 1.5k mine). I am absolutely sure it's 1.5k in mine, so maybe a simple mistake on his part?
Another possible problem is the 2 or 3 watt resistor between 220uf/450V cap ad the power 100R/7W resistor. This cap is essentially baked to the point that it is hard to discern the colors on it. It is either 4k7 as the 1st schematic shows or 4k3, maybe.
BTW, I found some terrific online sites which make reading resistors easy, just enter the color bands and it gives you the value - site 1(for 4 color) & site 2(for 6 color).
Odds are, that I am going to simply redo the amp point-to-point on new perf board with mostly new caps and resistors. The layout seems fairly simple and there quite a few low grade parts that ought to be replaced while I'm in there. I'll have more room to work in the replacment parts, all the HV resistors are extremly close to caps. And I won't have to worry about potentially bad traces. First, I'll be replacing the 50k Alps Blue potentiometer with a new PEC carbon pot from DiyHiFi Supply.
Russ57: Looking at Panasonic TS-HA or TS-HB 2220uf/400V caps for the 6 power supply and possibly the 47uf/100V EL-34 cathode bypass caps. Good suggestion on the Mills 12 watt for the two cathode bypass resistors, maybe even their heatfins, too. Hopefully, I can affordably improve most or all the marginal points you've noticed.
Shermanr, Unclestu52, Anthony, an AnandR: Thanks for the in-depth explanation of how a runaway tube works, I had no idea. That sounds like the most logical situation. Only the left channel 100R UL resistor fried, but the PCB under the two 47k/2W plate resistors is scorched brown. Right next to them, the 4k7/2W PS resistor got hot enough to bake the PCB, itself, and part of the 0.33uf EL-34 coupling capacitor. The area under the second 100R/7W PS resistor is also baked brown.
How do I check the transformers for damage?
Gingertube: Great explanation, even I could understand it. I'll put your advice to good use.
Finally, for beginners(like me) Express Schematic is free circuit software that makes everything incredibly easy. I installed it and hasmost of the circuit below finished in an hour or so. Be sure to download and install Gary Pimm's custom Express Schematic components for tube circuits. Just download Gary's zip file and extract it to "c:\Program Files\ExpressPCB" (for Windows users). It will overwrite the existing empty folder. Restart Express Shematic and all the tube symbols will be in the Component and Symbol manager under "Custom components".
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Follow Ups
- Thanks Everyone! Amp disassembled and revised schematic... - darkmoebius 23:33:37 04/30/06 (0)
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