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Traynor Mark 3
#1
After re-reading the tube amp FAQ on the LP website, I got a hankering to modify a Traynor Mark 3 with the standard preamp (LPSP). I found a reasonably priced combo in which the stock speakers were replaced by a pair of 16-ohm Jensen Nighthawks. The stock 

The stock speakers are 8R in parallel, so I'd like to know whether the Mark 3 can withstand this impedance mismatch.
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#2
Hi jmcd

Remember that impedance "matches" are only nominal.

Were speakers constant-impedance over frequency, then a (load to tap) match provides maximum power bandwidth. A mismatch always results in less power with a tube amp. But... speaker impedance changes radically over the audio band so no worries here.
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#3
I replaced the dynamite-stick filter caps with modern electrolytics rated for the same voltage (450V).

B+ is right around 452 Vdc, and so I'm concerned that I don't have enough "safety margin' (even though the original 450V caps lasted for 45 years or so). Should I install a pair of 250V in series for the first reservoir cap?

Amp now sounds much stronger.
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#4
(01-06-2019, 12:12 AM)jmcd Wrote: I replaced the dynamite-stick filter caps with modern electrolytics rated for the same voltage (450V).

B+ is right around 452 Vdc, and so I'm concerned that I don't have enough "safety margin' (even though the original 450V caps lasted for 45 years or so). Should I install a pair of 250V in series for the first reservoir cap?

Amp now sounds much stronger.

I'd be worried about it. My guess is that the voltage is higher than it would have been when wall voltages were lower but I'm not a Traynor expert by any stretch.   You could use higher voltage caps or caps in a series.  Another possibly would be to add a voltage clamp circuit or kit  to it to ensure the voltage will not be too high. I'm sure Kevin will have some thoughts on it too.....
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#5
I was going to edit my post to say, "I guess I should increase the voltage capacity", but since makinrose replied already, I'll leave my post as is.

I'll continue to focus on the power supply and grounding, and then I'll turn my attention on the preamp....
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#6
Hi Guys

As TUTs state, the voltage rating on an electrolytic cap is "working volts DC" and older caps have WVDC right after the voltage number.

So, 452V on a 450V cap is absolutely nothing to worry about.

As other posts on this forum and TUTs state, the notion of having "voltage headroom" or "excess voltage rating" for an electro is specious, as the cap reforms to the voltage present over time.

Have fun
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#7
The B+ was up to 457V today. Still absolutely nothing to worry about?

Thanks for the input, fellas!
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#8
Hi Jmcd

makinrose's point about the mains compatibility stands for most "vintage" gear like old hand-wired Traynors, Tweed / black-face - silver-face Fender amps, etc. inasmuch as those amps have PTs designed for 115Vac or 117Vac mains. Today the mains is more typically 120-125Vac, so we see a bump in the internal voltages by a similar factor.

Traynor uses Hammond PTs which were rated for 11Vac. If we suppose the applied mains is 125V then the voltages will all be higher by a factor of 125 / 115 = 1.087. So an expected 420Vdc becomes 456Vdc.

I spec my dual-range primaries as 120V and 240V, and the universals as 100V, 120V, 240V. I spec the heats to be 6V and 12V and leave off the fraction as all of this combines to keep the heater voltages within their ratings, rarely being higher than spec.

With new caps in place, I don't believe the 457Vdc is an issue on a (non-IC) electrolytic.

Of course, to contradict myself, I did go to 500V caps when a new batch of PTs resulted in 465V. Jmcd's 7V over is just 1.6% and my 15V over is still only 3.3%, but my amp might end up in India or some other place where mains voltages are wildly erratic, ie.e. 260Vac is not uncommon and this represents an over-voltage of 8.3%.
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#9
The mains power in my own home is usually 120V (1.043); that makes sense since the YGL3 schematic lists the B+ as 436V and I'm getting 455V on average (and on my latest reading).

Before KOC's posts, I had already changed the first reservoir cap to a pair of 100uF units in series, but I think that I'll keep using a 450V cap for the screens node.

As an aside, I created a simple PCB that holds two 18mm-diameter caps and a dropping resistor (or jumper, if the caps are to be placed in parallel on the same node). I'll use at least two of these in this Traynor.
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#10
I stand corrected. I hope I didn't cause too much extra work JMCD. I do tend to be little paranoid about such things.

It has led me to a question: is the voltage withstand of components different from the working voltage? So when tubes are pulled out an the voltage goes up from a lack of loading on the power supply what is safe amount or voltage to go over with say a 450V cap?
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#11
(01-08-2019, 05:50 PM)makinrose Wrote: I stand corrected. I hope I didn't cause too much extra work JMCD.  I do tend to be little paranoid about such things.  

It has led me to a question:  is the voltage withstand of components different from the working voltage?  So when tubes are pulled out an the voltage goes up from a lack of loading on the power supply what is safe amount or voltage to go over with say a 450V cap?

Work is fun. No problem there, makinrose!
I seem to recall KOC saying that ecaps are also rated for temporary over-voltages, but none of the data sheets that I looked at have such a specification. 

-- John
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