model-t: relation between warmup-time and sound?

[thomas]

hi. is there any relation between the warmup-time of tube-amps and the sound after switching it on? i had issues when it made a difference between 30secs. and 1min.. i have a 70s sunn model-t. sometimes it sounds great and heavy sometimes not. i´ve noticed a difference when i change the standby-time. isn´t that strange? when i put it on after around half a minute it sounds great, anything real longer than this sounds flat and harsh in distortion. a friend of mine has a marshall jcm-612 and he let his amp on standby for around 15mins.! i´m sure the cab can´t be the problem. the amp must be in good shape. it´s retubed and serviced well. help would be cool. greets

[JoeArthur]

This is not meant to be sarcastic Thomas, but what you are experiencing may be a simple case of imagination.

Consider this... most guitar amps, even the Model T have no real need for a standby switch.  The benefits of safety and longer tube life... etc, do not really pertain to the relatively low voltage operation of receiving type tubes like the 6550.  Transmitting type tubes that are operated at a high voltage (e.g. 1kv and higher) can greatly benefit from having the tube at full operating temperature before the application of this extremely high voltage.  

The standby switch on my Model T is always on, meaning in the operate position.  I turn down the master volume instead of flipping the amp to a standby mode.  If I believe it will be longer than 15 minutes I turn the amp off.

I don't have exact times, but there is a point in the startup/warmup as the cathode gets heated enough to start emitting electrons, but is not at full operating temperature.  The amp is "usable" but not at full operating temperature.  This can sound "weak"... and the volume will seem to gradually increase the more the amp warms up and the current flow capacity through the tubes increases.

The amp will sound it's best when it is fully warmed up and this usually takes mine between three and five minutes.  The warmup time can be affected slightly by the temperature of the air around the amp.  

But the time after the power switch is turned on... until you switch on the standby... this does not affect the warmup time.  So you may be trying to use the amp before it is fully warmed up.

[thomas]

i know what you mean. i wasn´t sure about it, so that´s the reason i asked. but can the sound of this amp be such various? sometimes it burns, someties it´s flat and stuff. the power-tubes are new svetlana 6500´s and preamps are new 12ax7a and a 5751 in the pi slot. i have heard things of this amp like "can be heard from miles" but that isn´t the case. i mean, don´t get me wrong, it´s loud and i play with ear-protection, but i could be louder.

[JoeArthur]

I'm not a real fan of the 5751.  Those that I have tried are too microphonic for my tastes.  One thing that you might be aware of, is that the 5751 has a lower gain (70-80) compared to the 12AX7 (100).  For this reason, I wouldn't recommend using one in the PI location, as the power amp feedback and related circuitry is designed around the higher gain.  I would swap it with the second stage where the circuit gain is less critical.

There are factors too numerous to come up with a complete list, that will affect how the amp sounds... and combine that with how you perceive the sound.  Things like choice of speakers, location of the speakers relative to the ear, placement in the room, the room itself and even the number of "bodies" in the room can change the sound... e.g. more bodies absorb more highs.

Personal preference and your mood can change how you perceive the sound... very subjective here.  Heck, my Model T sounds best to me when I'm frustrated and working out some anger!!

[thomas]

i changed the 5751 with the second slot 12ax7a and nothing different appeared. i mean this amp can´t even fuck with a 60watts marshall tube-combo and that really sucks. the overdrive is harsh and when i play single notes it sounds like fucking 80ies metal solos. nothing sweet. that really bothers me. i put lots of money in this amp and it´s like i did nothing. my last hope is my cab. it´s a ´78 ampeg v-4 cab with square mag eminences (don´t know the right name, they are maybe 75watts each, 1" voice coil), and i think this could be the problem. the speakers are in phase for what i know and  cosmetically in working condition. the cones are undamaged, too. maybe this cab is too "standard rock". there´s nothing clean or thick to it. maybe i should see if i can get some new speakers for it. greets