Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: TIMBO on September 12, 2014, 11:26:35 pm
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Hi guys, I've been on a mission help owners of much loved family organs put them to rest after many years of gathering dust. Yes I do tell them they are going to a better place. :think1:
This organ was a Hammond Everett Series 2200, It was only just working and on further inspection some of the components were past there used by date, so a few quick and painless snips and it was all over for this fine gent. :sad2: :icon_biggrin:
Goods BITZ.......
PP el84 power amp
Tube reverb
Some CC resistors
Some low voltage caps (coupling type)
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What's the model number on that EL84 amp? It'll be something similar to H-AO-60.
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Hey Sluckey, Just the man I want to chime in.
Chassis No. AO-48-3B.
I found a schem here https://archive.org/stream/Hammond2000SeriesChordOrganServiceManual#page/n0/mode/2up
I have redrawn a schem to get a better look at it.
And it looks good for your AC15 with reverb and tremolo :icon_biggrin:
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That looks like a nice donor amp. May I suggest firing it up without the rectifier tube to verify the unloaded PT voltages? If those look OK then plug in the rectifier but remove the output tubes and verify the unloaded B+ (May want to use a lamp limiter first).
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Hey Sluckey, I did a quick check of the Ecaps and they are all over the place in there value. There is no fuse on the mains, so I was a bit weary of turning it on with outdoing a few things first.
Seeing that the reverb and tremolo is already done I will leave it as is.
I guess all I need to do is insert a TS and connect the tremolo into the circuit as it is connected to part of the SS circuitry.
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Hi guys, how time flies, this one has been sitting on the shelf for far too long.
Trying to do as little as possible to stray from the original circuit, I've come up with this.
(https://i.imgur.com/qYJckSY.jpg)
(https://i.imgur.com/ZqcZCjT.jpg)
(https://i.imgur.com/0Qvo7BV.jpg)
Thoughts on how this will work. :icon_biggrin:
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Hi guys, Full steam ahead.
After many hours of snipping out components.......
(https://i.imgur.com/MD6CITR.jpg)
Still plenty to do, also remover the CC plate resistors and put in CF resistors.
(https://i.imgur.com/CMMu1lQ.jpg)
A bit of extra metalwork for the control panel.
(https://i.imgur.com/ifwttKZ.jpg)
The IRF820 mosfet close to where it is needed.
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Some progress....
(https://i.imgur.com/b38el8d.jpg)
(https://i.imgur.com/ZurPADj.jpg)
(https://i.imgur.com/P4D0UaM.jpg)
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Hi guys, This one has fired up well....
(https://i.imgur.com/gpA8BOe.jpg)
I did not have a 12DW7 so subbed it with a 12ax7 (reverb) and seems to be working well.
Also a mute switch was added to the "speed" control ground.
Again the trem is working to an OK level
(https://i.imgur.com/BuZwROM.jpg)
(https://i.imgur.com/wAjjVae.jpg)
Voltages look good.
(https://i.imgur.com/Y4LUcxb.jpg)
A well organized rats nest.
(https://i.imgur.com/3U4aMNM.jpg)
(https://i.imgur.com/8B7dWFj.jpg)
Looking to add Da Geezer's boost switch from the HoSo 56
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Hi guys, did a test run on boost circuit and seems to do the job, although when switching out the 390p cap it didn't really have much of an effect. :think1:
I'm sure this has been discussed, but I was trying to avoid doing the switch with a relay and just have a switch (foot) at the end of 4-5m lead.
Not having many volts on the lead and no major effect on the amp should the lead be damaged or broken.
What do you think. :think1:
(https://i.imgur.com/Kig69LZ.jpg)
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> 390p cap it didn't really have much of an effect.
What effect did you expect?
390pFd against the 1.2K resistor is 300,000+KHz; little happens at lower frequency. There's gain inside the loop so there could be some effect. It is positive feedback so the effect may be odd. As an extreme it could squeal, above the audio band. My gut says there's not enough gain to get into trouble.
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Thanks PRR, I'm sure Geezer did plenty of experimenting with this boost setup, so I'll take his word that it does what he intended it to do. :icon_biggrin:
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Hi guys, Found a neat little 5v relay board. Rectified a 3.2v heater tap and works well.
(https://i.imgur.com/cclck3Z.jpg)
(https://i.imgur.com/wkPKZ5h.jpg)
I have played around with the "boost" component values and found a 2.2uf bypass cap on V2b and a 470p cap at the top of the treble pot seems to do the job. These components can be easily changed now that I have the relay in place.
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Just a note... If you put the footswitch jack on the ground side of the relay coil you will not have to use an isolated jack.
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Thanks sluckey, I see that now.
The footswitch has a LED indicator, when the footswitch is "OFF" (relay disengage) the indicator is "ON" and is powered by the hot side of the relay.
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Head cab made and ready for tolex.
(https://i.imgur.com/Lnvad4J.jpg)
(https://i.imgur.com/Lm4eZC7.jpg)
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Hi guys, This one is done and gone to a good home. :icon_biggrin:
He is chuffed with the diversity and touch sensitivity of this "ODDBALL" amp.
And asked the question "what makes the oddball's sound so unique" :dontknow:
(https://i.imgur.com/4X6FkaR.jpg)
(https://i.imgur.com/bX440Nz.jpg)
Big thanks again, another happy customer. :thumbsup: