reel to reel tube amp

[Low low]

Grettings to all the tubeaholics. I am an old guy with a new, keen interest in tube power. But even though I have alot of age behind me, I'm a raw rookie when it comes to tubes. Love the sound, but need to learn everything. I recently acquired an old Crescent tube powered reel to reel in disarray. While it's missing some pieces on the outside, the amp and everything inside is complete. I'm assuming this would be a simple mono amp? And if so I am wondering if this little amp would work with an old Trio tuner I also have? Like I said, I am a newb at tubes, but would love to learn with something cheap. I can try and post pics if that would help? Any assistance would be appreciated.
Tom

 

[RWood]

Greetings and welcome. I would hazard a guess that the Crescent could almost certainly used in this capacity. It might not be the easiest first project, though, because reel amps are sometimes laid out less linearly than typical audio amps, using up available space inside a tape recorder chassis and case. There are exceptions, like the Akai/Roberts and Ampex amps. So please do post a pic of yours.

It is also easiest to do if you can get some documentation on what you are starting with, ie a schematic diagram. So do some googling and see what comes up.All that said, though, if you list the tubes that are used in the amp section chances are that we can still help you.

Where are you located?

 

[BmWr75]

Post some pics.

 

[Low low]

Here's a front shot of the amp. The tubes are as follows: 12au7a, 12ax7, 6x5gt and 6v6gt.

 

[RWood]

Oh heck yeah, that looks like a really good candidate. Is there an output transformer mounted to the speaker?

What model is that?

 

[Low low]

Whoops! Accidentally posted one for the visually impaired. Have to try and fix that. I'm from Edmonton Alberta, Canada.

 

[Low low]

No output transformer. It had 2 speakers that were simply run in parallel. The Model number is TR-722. I have the schematic glued to the lid.

 

[cubby01]

Well, top side looks pretty straight forward. How about a bottom shot. I assume there's a small output transformer under there somewhere. ??

EDIT, late to the post. I see you answered already. How about a photo of the schematic. That would be a great assist. I can't quite imagine not having an output transformer. Those speakers would have to be quite the impedance.

 

[cademan]

Its gotta have an output transformer somewhere. Maybe under the chassis? If no output transformer then you would have to use the original speakers that may be 500 ohm or such.

Tubes use output transformers to couple them to speakers otherwise the ohms would be way too high to drive any conventional speaker. Some exotic amplifiers are built with no output transformers but then the speakers are either high ohm speakers or the amps are designed to handle 4-16 ohm loads.

 

[Low low]

Bottom shot.

 

[cademan]

There it is! Bottom right hand corner. :yes:

Also, no need to replace any capacitors under the chassis as they are all ceramic disc capacitors. These are hardly ever problematic or go bad. The only one that might need to be replaced is the single can capacitor on top of the chassis.

 

[Low low]

Made the schematic a little bigger for easy viewing

 

[Low low]

I should mention that I am just beginning to learn how to read these schematics. Have to admit that initially it looked like a foreign language. I acquired a variac, which I've read is quite handy when restarting old tube gear. It's nice to know that I won't have to mess with too many capacitors for starters. I'll show my ignorance once again by asking where one would look to hook up inputs for various devices(tuner, tape deck, etc)?

 

[cademan]

According to your schematic, your amplifier has a jack for radio/phono. This is the one to use with your tuner. Do not use the microphone input jack but since you may not be sure which jack is which, you can try both but just make sure your volume is down as the microphone jack will be distorted at any level. It won't really hurt anything but the mic input is just a lower impedance input than what a CD player, tuner etc normally puts out.

It looks like you only have three jacks so one would be for the external speaker, one would be for the microphone, and one would be for the radio/phono. Simple!

 

[rcflybob]

There it is! Bottom right hand corner. :yes:

Also, no need to replace any capacitors under the chassis as they are all ceramic disc capacitors. These are hardly ever problematic or go bad. The only one that might need to be replaced is the single can capacitor on top of the chassis.

It looks like there is a small 25mfd cap in the lower left corner, shouldnt be a problem replacing it though as it looks pretty accessible.

 

[cademan]

YUP, I just saw that one and only lonely capacitor all by itself.

 

[Low low]

Just went hunting and found the top plate that indicates all the controls(forgot I even had it lol) The outermost jack on the left says mike. The one beside it is marked phono/radio(feeling kinda dumb right about now) and the jack on the extreme right says ext speaker. So would I be wise replacing these two caps before proceeding? Or could I go to the start up process with the variac? I've read that the rectifier won't allow a current until a certain voltage is reached. Does this mean that the amp wouldn't really benefit from lower voltages?

 

[Low low]

Just pulled to lid on the old tube tuner. Couldn't believe this little fella(which weighs alot)would have so many tubes(8).

 

[cademan]

I would go ahead and plug it in. I have not experienced any catastrophic failures in 40 years of electronics repair except maybe one or two where the can capacitor was shorted but still very repairable.

Within the first minute or two, just watch the 6X5 rectifier tube for any inside sparks and make sure the can capacitor does not get warm or hot within the first few minutes. If either of these occur, simply power down and don't power it back up until you have replaced the part causing the short.

Tube amps are way more rugged than solid state stuff and will take a lot of abuse including shorts (temporarily turned on of course) and will keep on ticking. Sound familiar?

By the way, they knew how to make tuners and amplifiers back then. That tuner might just outlive you and me!

 

[rcflybob]

That Trio tuner is in very nice shape. Bet it will sound very nice too. Just be careful with tube gear, its like a quicksand pit, once it has ahold of you it will suck you in and there is no getting out of it.