power loss in '66 blackface princeton n/r

[tomfarnan]

Hi, I'm getting a big power loss in my Princeton non-reverb amp when I crank the volume up to 7 with my telecaster. The output volume takes about a minute to get back to previous levels. The preamp tubes are new but the output valves (6v6's) are quite elderly and don't appear to be matched. Could the output valves be in need of replacement?

Is it likely to be transformers or capacitors or anything more complicated?

Thanks in anticipation,
Tom

[mikeboone]

You should surely replace the 6v6's if they are that old and unmatched. It is most likey the issue, and if its not, you'll need them anyway.

[tomfarnan]

ok ... replaced the 6v6's and the rectifier tube with new JJ electronics tubes. I'm still losing power when i play into my tele at volume.

If I play hard the power dies away. I think I might need a step down transformer that handles more than 0.57 amps.

[qwixzh]

So you are using a step-down transformer. Is this capable of handling the total power requirement of the amp?

You can monitor the output of the step-down transformer. While playing hard, does the voltage output goes below than expected? If yes, you should change your step-down transformer.

Hope this helps.

qwixzh

[MWJB]

Fender rates the Princetion at 125W consumption, what's the rating of your step-down?

[mikeboone]

If the Princeton requires 125W at 115 volts, you will need a step down transformer that is capable of over 1 amp

You stated that yours is .57A. Is that the current it can source on the stepped down side? I am assuming yes.

You should so as qwix recommends and monitor the AC voltage while you are are playing hard. If your AC input V drops during this time, then everything past it will drop as well. Lower plate V means lower volume.

But hey - You got some new tubes now!!!

Have fun.

[tomfarnan]

thanks for all your support! I seemed to have solved it with your help and some chatting with a local repairer - the step down transformer is too small. I solved the problem tonight once and for all and bought a Mercury Magnetics Princeton Blackface 240V power transformer which I'll have installed in several working days' postage time. US tube amp buyers should count their lucky stars that they have access to such a huge amount of interesting and affordable amps and guitars!

Thanks again, tom