Amp Tubes / Using Preamp out

[silentbry]

I guess I have two questions.

1) How do you know really when to replace your tubes. I've had a fender blues deville for about 10 years and never replaced the tubes. Also, where is the best place to buy/and find the right tubes for a specific amp? (ebay, a different online store?)

2) I've been using my amp to record w/ directly into my protools computer system. I've been taking the guitar signal out of the preamp to go into my hardware interface. I have DISconnected the jack on the back of amp that goes from the amp guts(head) to speakers. Is this bad? I just recently read that this is not good to do because it leaves no where for the resistance from the tubes to go?

Thank you in acvance.

[Mars Amp Repair]

1) How do you know really when to replace your tubes. I've had a fender blues deville for about 10 years and never replaced the tubes.

A) 10 years? I'd say it's time...even if they've only been idling, you don't want to wait until they short & take other things out.

2). I've been taking the guitar signal out of the preamp to go into my hardware interface.

A. does the amp still have the original speaker jack installed...if so, disconnecting the speaker plug might provide short circuit termination auromatically.
You definitely need to terminate the speaker out jack in some manner as tube amps become unstable with no load but at the same time you don't want to be driving the power stage into a short.

One solution would be:
I think this amp has a 'power amp in jack' that cuts the drive to the power stage (much like a return jack). You could just put a dummy jack in there when you're recording & unplug the speaker. If the jack is not the shorting variety, you could put a shorting plug in the speaker jack.
glen

[Ptron]

1) How do you know really when to replace your tubes. I've had a fender blues deville for about 10 years and never replaced the tubes.

How much has the amp used? Tubes wear out with use, so if the amp is rarely used, they could be ok. Also, the power tubes take more of a beating than the preamp tubes.

You could just put a dummy jack in there when you're recording & unplug the speaker.

Mars, are you talking about using a shorting 1/4" in the power amp in? If so that would quiet the speker without having to unplug it, wouldn't it?

[silentbry]

to answer some of your questions to me:

-The amp isn't really used that much overall. but I'm using it a lot more just for recording thru it.

-Yes, the amp does still have the original speaker jack. nothing is modified on this amp at all.

-when you say use a 'dummy' power in cord for power amp in, do you mean just stick in a quarter inch cord not coming from anything else?

-so, just so I understand you guys (I'm not a big tech guy!), in your overall opinion you do Not think it hurts to go out of the preamp, and have the speakers unplugged?

-also, my clean channel (which I never really use) 'breaks up', doesn't sound clean, is that a tube issue?

thanks you guys.

[Tom Phillips]

You are asking the right kind of questions silentbry and, yes, it can be confusing.
Glen and Ptron’s responses contain the information you are looking for but I’ll jump in now so you will have a summary answer right away in case they don’t get back here for a while.

so, just so I understand you guys (I'm not a big tech guy!), in your overall opinion you do Not think it hurts to go out of the preamp, and have the speakers unplugged?

When the speaker is unplugged from the Blues DeVille, the internal switches in the speaker jack short the output of the amp. This prevents high voltage spikes from being generated in the output circuit of a tube amp if someone tries to play the amp with the speaker disconnected. This is a protection designed in by Fender but it can still be hard on the power section as the amp tries to drive a short. It’s better for your amp to have the proper load connected whenever a signal is present.
I recommend that you leave the speaker connected. AND …read below…

…when you say use a 'dummy' power in cord for power amp in, do you mean just stick in a quarter inch cord not coming from anything else?

Good idea from Glen.
I checked the Blues DeVille schematic and this will work.
You make a shorted dummy plug out of a standard ¼” guitar plug by connecting the tip to the ground lug. Use a short piece of wire soldered to the lugs not just twisted around them. Plug this into the “Power amp in” jack. This will open the signal line between the pre-amp and the power amp. The short in the plug will eliminate bleed through and make sure that the power amp will stay quiet.

You can now play into the amp and take your signal from the “Pre-amp out” connector.
When you want to use the amp in normal mode just remove the shorting plug.

Have Fun,
Tom

[silentbry]

man, thanks for all the info.
I've got another probably dumb quesition then. what do you mean by 'ground lug'?

and just to be clear, you're saying that fender has designed the amp to protect itself when the jack to speaker's aren't plugged in. so, it is probably ok to continue doing what I've been doing(playing out of preamp w/ speaker jack disconnected) , but just Not recommended. ..because something could happen.

thanks again everyone for your help.

[Tom Phillips]

…what do you mean by 'ground lug'?

I meant the part inside the plug that’s connected to the sleeve of the plug.
See page 26 & 27 of the manual at http://www.aphex.com/pdf/207/Aphex_207_user_manual.pdf for example illustrations of phone plug wiring.

… you're saying that fender has designed the amp to protect itself when the jack to speaker's aren't plugged in.

They added some “protection” to cover temporary mistakes.
IMHO that's not enough to protect the amp indefinitely when it’s deliberately abused.
Think of a motor cycle rider who dumps his bike and is protected by the leathers he is wearing as his body skids across the pavement. He may be protected for a while but if he keeps doing that the leather will eventually get worn through and he is no longer protected.

…so, it is probably ok to continue doing what I've been doing(playing out of preamp w/ speaker jack disconnected) , but just Not recommended. ..because something could happen.

Depends on what you mean by OK. It wouldn’t be OK if I caught someone doing that to my amp. The OT is trying to drive power into a short, the output tubes are working really hard and all the energy is being dissipated as heat inside the amp. All high stress that's not necessary.

Regards,
Tom

[Mars Amp Repair]

Thanx tom for clarifying that...sometimes it's difficult to strip out all the techy stuff & get down to the "Just tell me what I need to do" level.

Bottom line for me here would be;

1. Install the shorting jack to the power amp in jack to keep the signal from driving the power stage.

2. although optional, I would still disconnect the speaker to keep any inherent noise from coming out the speaker ie;hiss, power spike pops, etc.

3. The ultimate solution (the techy solution): the power tubes will still be drawing the idle current even if the signal is removed with the shorting poweramp in jack. For maximum power tube life & also much less heat from the amp, you could consider having a tech install a 'cathode disconnect switch' for the power stage to effectively stop the idle current in the power tubes. The power tubes would last much longer.

In that scenario, you wouldn't need the poweramp in shorting jack or to disconnect the speaker...just flip the switch. glen

[Mark Black]

And perhaps a low-tech no-solder solution:

Remove the power tubes when using the amp like that.

Although I must say I'm not a big fan of exercising the contacts in the tube sockets that much...

Mark

[silentbry]

thank you thank you guys for all your replies and info.

I'm taking it all into consideration. now, I have one question. I am a horrible 'tech' guy as far as soldering and things like that go. as far as something I could buy that could help me out w/ recording thru my amp, what is a good purchase? I know there is the THD hot plate and things like that (which can also get pricy). any good affordable solutions you know of I could just buy? thank you again and again!..

[silentbry]

or, is this a safe solution?: going into my amp input w/ my guitar, out of the preamp out of amp into my boss tuner(which has two outputs, one bypass, one tuner out), take the tuner out back into the power amp in(which I believe is just like the 'effects loop return on my amp) while leaving the tuner on(this will mute the sound to the amp), then take the bypass output of the tuner into my recording interface. follow that!? ok. thanks everyone. just trying the cheapest way to get my amp sound, w/ out mic'ing it , doing any soldering....

[Tom Phillips]

The pre-amp out / Power amp in as implemented in the Blues De Ville is basically an FX loop. Your tuner hookup description should work. Give it a try and, if you are satisfied with the sound quality, you are home free.

One other thing to consider about the tone you get by taking your signal from the pre-amp out is that you will be missing the tone shaping / filtering effect of the speaker. That will require some additional EQing. Especially to tame the high end.

Have Fun,
Tom