Quantum Bass

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Much delayed, I present to you, Mr. Kidder's Quantum Bass. Unfortunately, much delayed due to events beyond my control. It will be recapped, retubed with nos 8417's and have a three prong plug replacing the two pronger.

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Signs that it was dropping too much current. In the lower right hand corner, there are two 6.8 ohm resistors that are burned, as well as the wire (NFB?) running next to them.

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<edit> Fixed images
 

capnjuan

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Eh ... I don't think this is what you had in mind ... :? :p
 

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:oops:


Has a mix of Telefunken, GE and RCA 12ax7's as well as the requisite 7247 phase inverter.

As has been reported by our esteemed capn, the preamp circuitry is located on 3 pc boards.

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All of the small blue 30 mfd caps look to be original, i.e. dried up. Those will be replaced as well.
 

capnjuan

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Thanks Steve; the chassis shots ... those are the 'before' pics? If yes, what did you wind up using for the primary filter caps? The fiippy dippy with the little boards is no fun but those old cathode caps can't stay either.

Of all the Guild heads in the post-Avnet era, I thought this one with its beefy power supply, use of the 7247, and the screen regulator ... this one was ready for prime time ... more about this amp in this thread.
 

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Thanks Steve. Bit of an early Christmas present for me to see it coming.

I'm off to Norway for Christmas with my kids - not so easy since my wife's death last December 18 - will look forwrd to some big notes from the amp in January.

Merry Christmas to you - hope all is well.

John
 

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john_kidder said:
Thanks Steve. Bit of an early Christmas present for me to see it coming.

I'm off to Norway for Christmas with my kids - not so easy since my wife's death last December 18 - will look forwrd to some big notes from the amp in January.

Merry Christmas to you - hope all is well.

John

:(

Looking forward to getting it back into your hands. Unfortunately, the combo of complete lack of workspace and some other issues left it untouched for the past bit.
Capacitors
250 mfd 500 volt capacitors are in stock at AES. The wonky bias cap (single positive, two negatives) is being replaced by separate caps. The 40/40/40/40 cancap is being replaced by a 20/20/40/40 and I'll add a couple of separate 22 mfd caps to make up the difference.

John, where did you source those 6.8 ohm 1% resistors for your rebuild?
 

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Finished! Biased the 8417's at the correct .3 volts, set the screen voltage regulator to the correct 300 volts. Installed a proper standby switch. Bunch of pics to upload in a day or so. Unfortunately, I just have a tele with a bad jack to test it out with. In a basement full of transformers. :roll: BTW, I'm the king of 6.8 ohm, .05% resistors. Need a couple, pm me your addy. :lol:


529 volts on the plates!
 

capnjuan

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Much delayed, I present to you, Mr. Kidder's Quantum Bass.....
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... as well as the wire (NFB?) running next to them.
Yes; looks like the negative feedback. For those following along on the home version of this game ... to stabilize the signal, the amp's output is tapped and part of the signal is returned to the first stage of the 7247 through an R/C filter. In some amps, there's a switch in the loop switching the R/C filter in or out of the loop ... in Gibson-speak, 'Tone Expander' ... 'Presence' in some other amps.
8417nfba.jpg
 

john_kidder

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I am just plain excited about plugging in to this new old machine.

Thank you Steve for all this work, and John for commentary (and suggesting Steve in the first place).

Marvellous.
 

capnjuan

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My pleasure John; had things been different, I would have taken care of it for you in a heartbeat.
 

capnjuan

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Which is a helluva lot quicker than I've been with this. :roll:
Eh ... more like I wouldn't have hesitated to take it on ... how long it would have taken would have been anyone's guess. :wink:
 

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Oh, while my brain is screaming at me to sleep. :wink:


After digging into the Quantum, I'm not convinced that a 40x4 can cap is necessary. one of the 40mfd sections just feeds dc to the hum balance control...
 

capnjuan

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Oh, while my brain is screaming at me to sleep. :wink: After digging into the Quantum, I'm not convinced that a 40x4 can cap is necessary. one of the 40mfd sections just feeds dc to the hum balance control...
Weber no longer offers a multi-section can cap but I think the owner of Wuzzatronics Sound Labs NZ has a 4X40uf@450V ... in an attractive shade of blue.
 

capnjuan

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I'm just not sure that 20 mfd wouldn't be adequate.
Don't disagree; besides, no one's really sure where NZ is anyway :)
 
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