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there has been a homemade outlet box variovac in Dynaco on Ebay. It takes 123 volts on your outlet and brings it down to 115 volts and 108 volts for each plug on the box. The maker made it for the Dyna 70 transformer which he says runs optimally at 115 volts....is there anything to this? Could this 8 volt difference effect transformer humming?....I hope the ebay picture goes thru but if not the box is on the Dynaco catagory.....thanks for any ideas...Mark Korda
I don't know about the 70, but the Mark III's have a problem where the B+ exceeds the PS capacitor voltage ratings until the outputs warm up enough to conduct. The fix is a thermistor. If you search Dynaco inrush current limiter you will find a lot about this, including the 70.
While the specific voltage of design versus what comes out of the wall can be an issue -
My experience is that less than 10% difference is ignore-able
Furthermore- my concern with the device pictured below OP - looks to have a very limited current capacity (based on size) even though the assembler used 20A receptacles.
The ad reads " uses a new hammond bobbins transformer rated at 4 amps " and he installs a 3A fuse to (hopefully) keep users from exceeding that.
Certainly not a universal bucking transformer, but it should work OK for a vintage Dynaco ST-70. I wouldn't try using it with a pair of MK-IIIs though.
A little more costly but a better solution if you are concerned about the transformer. The original was marginal as it is. This one is more robust and can delivery the current needed during heavy peak loads.
I remember, quite some time ago, reading that a noted Dynaco expert and builder (was it Bob Latino?) mentioned that Dynaco transformers were designed and made for 115vac and tended to have some longevity problems when run using the modern 123vac standard.
I'm not the one to make recommendations on electronics but I'll pass along something I read for a DIY inexpensive voltage drop. Find a short extension cord, something like 6' or so. Separate a short section of the two leads and cut one. Trim the insulation back and wire in a standard light socket. Insert a 30-40 watt bulb. Connect the component to be turned on and the cord to the wall. This will not be variable but will reduce voltage passing to the device. If this is a valid method maybe someone can suggest how long this should be left on before reconnecting the component directly to the wall?
Even buying new parts should cost only a few dollars, not $110.
"The piano ain't got no wrong notes." Thelonious Monk
is used to power up a piece of electronics which has been in storage for a long period of time, to allow the capacitors to reform, hopefully without self-destructing.
That ebay bucking transformer is meant for constant use, to drop the AC wall voltage from today's higher averages (> 120 VAC) to 110 or 115 for devices which were designed to use lower voltages.
You're right that someone could DIY one for themselves fairly inexpensively if they know which end of the soldering iron gets hot, and feel safe with wiring projects.
thanks you guys for all the info. I do have a nice Variovac I bought a few years ago. I have slowly warmed up old vacuum tube stuff but never thought about the outlet voltage.
That Variovac, the home made one, caught my eye when the builder told why he made it.
I have 2 nice Dynas I love but they have a small hum to them. I have tried losts of experiments and even bought a Emotiva power strip with 2 outputs to solve things. Out of all the answers I got from another forum no one mentioned the correct voltage from the wall outlet, even Van Alstine who suggested his devise which is like the Emotiva, the HumDinger.
So unless I get (don't waste your time) from someone I'm going to hook that Variovac up at 115 volts and report to you all on my audible findings. Theres no wrestling on tonight so it will give me a little project to do.....thanks you all...Mark K.
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