One more Eico ST70 rebuild thread
- Thread starter oldman55
- Start date
Its all good.
We're glad you're enjoying your eico
We're glad you're enjoying your eico
s-petersen
Scott
I'm also happy to see it working properly, it was touch and go for a moment there.
You really can't say this is how it should look everytime. Typically a DBT is a protection tool.
If a unit has a major fault (short) the unit acts like a light switch. Bulb at or near full brilliance instantly and stays there. If a unit has this condition its fuse will blow (hopefully) but leave you no powered testing options.
Ideally (with the proper sized lamp (lamps), at power on bulbs should be bright (brighter) instantly then dim until faintly lit (possibly dark, depending on unit , lamp size, overall brightness in room).
You are in essence creating a voltage divider network. 2 series impedance loads. The bulb mostly a fixed value (I'm sure its resistance (impedance) changes as the filament heats but for sake of simplicity we can call it a resistor. The unit normally would have a low resistance (impedance) at instantaneous power on, then as PS caps charge its resistance rises (caps become charged and it becomes less conductive. )
While it less than perfect, the bulb gives you a visual picture that the unit is powering normally. As a testing tool (this is less precise, because certain tubes must reach a certain temp to conduct but)
You can measure actual v in to unit and with some degree of accuracy test for percentages of voltages that should be present at certain points without risking releasing magic smoke.
To a degree with multiple lamp sizes (or possibly multiple bulbs you can adjust the voltage at the unit by varying bulb size (sort of a poor man's variac.
(Under some conditions its advantageous to run variac through DBT to unit)
Its also useful (to a degree) starting old gear. It gives the electrolytic caps a chance to reform.
Clear as mud right?
Seriously, if something isn t clear, ask.
If a unit has a major fault (short) the unit acts like a light switch. Bulb at or near full brilliance instantly and stays there. If a unit has this condition its fuse will blow (hopefully) but leave you no powered testing options.
Ideally (with the proper sized lamp (lamps), at power on bulbs should be bright (brighter) instantly then dim until faintly lit (possibly dark, depending on unit , lamp size, overall brightness in room).
You are in essence creating a voltage divider network. 2 series impedance loads. The bulb mostly a fixed value (I'm sure its resistance (impedance) changes as the filament heats but for sake of simplicity we can call it a resistor. The unit normally would have a low resistance (impedance) at instantaneous power on, then as PS caps charge its resistance rises (caps become charged and it becomes less conductive. )
While it less than perfect, the bulb gives you a visual picture that the unit is powering normally. As a testing tool (this is less precise, because certain tubes must reach a certain temp to conduct but)
You can measure actual v in to unit and with some degree of accuracy test for percentages of voltages that should be present at certain points without risking releasing magic smoke.
To a degree with multiple lamp sizes (or possibly multiple bulbs you can adjust the voltage at the unit by varying bulb size (sort of a poor man's variac.
(Under some conditions its advantageous to run variac through DBT to unit)
Its also useful (to a degree) starting old gear. It gives the electrolytic caps a chance to reform.
Clear as mud right?
Seriously, if something isn t clear, ask.
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I use an ammeter for this sort of thing. Its more repeatable than trying to figure out how bright the bulb is. Current load will depend on the amp, so you'll get different levels of brightness with everything. The dim bulb is more of a safety / sanity tester than a precise measurement.
Dandy
Addicted Member
Yeah, it's more like having someone beside you ready to shout, Whoh! Stop!
s-petersen
Scott
Between my variac and the piece I'm working on.
s-petersen
Scott
The meter and enclosure are on the auction site, total was around $10. The outlet was from a dead power inverter
I found it in this thread
http://www.audiokarma.org/forums/in...-the-team-digital-amp-volt-watt-meter.724611/
I found it in this thread
http://www.audiokarma.org/forums/in...-the-team-digital-amp-volt-watt-meter.724611/
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oldman55
Well-Known Member
Parts came in and did the phono mod along with the loudness mod. I added the new jumpers but left in the old ones, following NJ's photo, hope its right.
BTW, I ordered parts for several projects yesterday from mouser. They came in today. How they can double pack and label every 20 cent part and get it to me the next day is unbelievable.
Gonna case it and put it back on line. Something about the sound and power (and weight) of the ST70 that wont let it sit on the shop bench for long.
BTW, I ordered parts for several projects yesterday from mouser. They came in today. How they can double pack and label every 20 cent part and get it to me the next day is unbelievable.
Gonna case it and put it back on line. Something about the sound and power (and weight) of the ST70 that wont let it sit on the shop bench for long.
I get Mouser in 2-3 days, Digikey is a week if I order to my house, 4 days if I send it to work. I live 1/2 mile from work, in the same zip code, and am serviced by the same USPS, UPS and FedEx drivers. Its also cheaper to send it to work since it's a commercial address. Mouser makes no difference.
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