: : : : Why have so many older tube type amps had the power or output transformers replaced?
: : : John:
: : : Likely reasons include: operating the amp without a speaker connected, prolonged incorrect impedance match between output transformer and speaker, marginally designed output transformers and failures in tubes, power supply or parts around the output tubes. All of these can have adverse affects upon output or power transformers. Also, insulation on the wire within a transformer can break down over 30 years or so, causing internal shorts. Many amp manufacturers spec parts which have minimal overhead capacity in order to meet a price-point in order to be competitive in the market. Others are designed that way in order to achieve an over-driven sound. Mid-sixties Fender bassman amps had small output transformers that hit their core-saturation point easily. That made them notorious for "farting out" on the low E string. It also made them sound heavenly for over-driven guitar work. This was used to great effect by Jim Marshall his early amps. That's also why you see many early plexi heads with replaced output transformers (I've repaired one for a famous NW band that had it's output transformer replaced once already!). Hope this helps!
: : : Ryan
: : Ryan,
: : Thank you for the information. I totally agree with what you said and I relize that I aksed too general a question. I was refering specificallt to Sunn amps. In the 60's I noted that the mounting feet would fracture on the transformers due to rough handling. I was wondering if this was a common flaw or an isolated case. I was fishing to see if others had experienced the same problem.
: : Thank you for taking the time to reply.
: : John
: John:
: I have seen this same problem on many Sunn amps and even on some Dynaco hi-fi amps (most notably the Dynaco Mark III.....which the first Sunn "Smiley Face" amps were based upon). Sunn continued to source their transformers and filter caps from Dynaco in the late 60's. Check any early Sunn amp and you'll see Dynaco transformer numbers on the transformers and even see the Dynaco name stamped on the multi-section filter capacitors. The transformer "feet" often broke because of the light gauge metal that was used...designed for stationary hi-fi rigs rather than guitar/bass amps subject to frequent and sometimes rough handling!
: Ryan
Ryan,
You have confirmed my suspicion. I wonder how many transformers were replaced due to this reason. If the problem was'nt realized in time the weight of the transformer could eventually rip the leads from the windings. A good tech may be able to dig out the end of the windings and solder on new leads if possible, otherwise you would need a new transformer. I have seen replacement transformers (output) in Sunn amps that did'nt have the ultra-linear screen grid taps and the screen grid supply was derived through dropping resistors from one section of the power supply. I'm sure that this arranigment compromized the quality of the output circuit.
By the way, If you know what the numbers that Dynaco used to identify there transformers, I would sppreiciate it if you would pass that information along.
Thanks,
John
