Donor Organ #4

My Dad provided parts from a solid state Lowrey and Hammond, and Ron Ashcroft provided the AO-35 from a Hammond. Friday I retrieved a 1961 Conn model 541 "Minuet" in non-working order. This was listed in the free section of CL. Yes it is a tube job. The amplifier is actually a stereo power amp using two pairs of 7868. These amps go through two crossovers to drive two 15" speakers and a rotating assembly with a Jensen driver. I am thinking about removing this entire assembly complete. The photos show that each key is controlled by half of an 12AU7 and its own tunable transformer.

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Champ amp now in cabinet

I finally completed the Fender Champ project. Though the joinery didn't come out like I'd hoped, it turn out well enough. The front baffle was a sliding lid from the 1969 Magnavox console I stripped a couple of years ago.





If you look at the first picture to the right you might think I was way off on centering my handle. The handle isn't centered on the length of the amp, but on the weight. You can see why in the second photo.





In the third photo you can see the aluminum HVAC tape used for RF shielding, as well as the speaker scews used for mounting. The voltage plate came from the Tektronix ocilloscope I've been stripping.


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Cabinet for Champ and Build for Carmen Ghia

Long time since I last posted. I finally decided to put the Champ 5E1 in a head cabinet. I cut the 1"x10" boards with the intent to rabbet the joints, but I learned I cut them too short for that. Butt joint it is then. I hope to put a 3/8" routed edge on before adding a faceplate and finish.



Since I built the Champ using an old Soviet ammo can for a chassis, there were no flanges for mounting the chassis to anything. I had to cut flanges from joist/deck hardware, then notch the bottom lip of the chassis so it sits flush, before riveting the flanges on.


After ordering parts from TUBESANDMORE, I began modifying the Hammond chassis. I've mounted input and output jacks, Alpha pots, 110vac neon pilot light, switch, fuse holder, wire bridges (I think that is what they are called.) and power cord. The CG schematic is below.
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Repairing the Champ and Preparing for the Carment Ghia

I haven't updated this blog in months. At Christmas, I received some vintage tube gear from my father-in-law and some parts from another Hammond organ from my father. This has revived my tube amp work. I have finally replaced a resistor in the Fender 5E1 (Champ) clone I built. This resistor reduced my 6.3v secondary tap to 5v for the heater filament in the 5Y3 retifier. I believe the the rating on this heater is 2 amps so the resistor was taking a beating beyond its rating. This is visible in the first photo. I replaced it with the three resistors as configured in the second photo.


The Hammond organ parts donated by my dad were the two speakers, reverb tank, and the crossover visible in the third photo. All of this came out of a solid-state 1975 Hammond 9822J "Dolphin". These parts, along with the Hammond AO-35 amp, should produce a nice combo amp or possibly separate head and speaker cabinet. I haven't decided this yet. The Cleveland amp producer "Dr. Z" build his business by converting the Hammond AO-35 into amps he called the "Carmen Ghia". I hope to mimmick his circuit as best I can. The challenge will be working the reverb into the design, since the Carmen Ghia schematics I have don't have reverb in them.


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New projects complete and today's hamfest find

My last post was a while ago and in it I mentioned that I was starting new projects. I completed these using two more east European ammunition cans, just like I used for the Fender 5E1 build. The red unit is a high voltage DC power supply which will initially be used for reconditioning electrolyitic capacitors. The grey unit is a AC volt/amp meter which I built to use with the variac. Both of these will support the further tube work I will do.

The last photo here is of a purchase my neighbor Brian just made at the Hamfest we went to today in Milford, Ohio. This is a 1952 US Navy Ocilloscope. Very compact and light weight. He paid $20 for this thing!

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Final 5E1 changes and beginning of new project

In my last blog I described my problem with audible hum. My father instructed me to lower the DC in my circuit by inserting 550 ohms prior to the first filter capacitor in the power supply. I did this and also replaced the first two 8mfd electrolytic caps with a single canister electrolytic with two 20mfd taps. Hum dropped dramatically with these two modifications. On my father-in-laws recomendation, I also changed the wiring to put the fuse on the incoming line side of the 120ac, right before the switch. All of these changes and the resulting voltages are in the schematic to the right. A view of the amp with the added can capacitor is here. Don't forget to click on the images to see enlarged versions.

A group of articles proved most useful in understanding capacitors, power supplies, and reducing noise. My father provided three articles which I will scan into PDFs and make available in the future. The other articles are linked below:

Testing Capacitors
Restoring Capacitors
Repair and Replace Electrolytics
Replacing Capacitors in Old Radios

The next project I am starting will either be a power supply for reforming electrolytics, or another amp project. I have another old TV power transformer and ammunition can, as well as a pile of other parts left over from the 5E1 project.

Revised 5E1 Schematic

This schematic reflects the changes which I made as I built my project amp. Notice the hybrid rectification method using SS diodes and the 5Y3. Fender didn't see fit to show the 6.4vac feeds to the audio tubes in their schematic, so I added them. My 60hz hum is still present. I tied a 10mfd electrolytic cap in series with the second 8mfd cap in the power supply, just after the choke, and this reduced the hum by 50%. I am now testing an old 20mfd can cap removed from one of the console TVs I scrapped. If this thing is good, I will swap it for the 8mfd that is in place now. The voltage values in red are what I actually am reading with the amp powered on. I will adjust this with resistors later. Don't forget to click on the image to see a larger version, or click on the link below to go to the actual blog.