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.

Fender "Champ" 5E1 is finished!

Well...mostly. Earlier this month I completed the assembly and began testing. Since then I added a switch for the feedback loop which runs from the output transformer back to the cathode of the 6V6GT. Since the power transformer does not have a center tap for the HV secondary winding, I wired a diode to each leg of HV windings and then tied the other end of the diodes to ground. The HV windings were then wired to the 5Y3 as per the schematic. It is my understanding that these diodes working with the 5Y3 provide full-wave rectification. I will post a revised schematic soon, but for now will include these photos. Don't forget to click on the photo to see a larger version. The first photo above shows the external components and where they came from.The Second photo shows the inside of the amp from the bottom. The wiring looks cluttered, and is, but I do have star or central ground and all grounded components are tied to this via the dark green wires. The other noise reduction effort involved using a cordless drill to wind the 6.3VAC heater wires which are light green. Since all of the components are pulled from scrap (except the output transformer, filter caps and cathode bias caps), I had to approximate values by combining parts. There are several resisters tied in series to achieve the proper resistance, and you can see two caps tied in parallel (yellow at bottom left) for the coupling from the 12AX7 plate to the 6V6GT grid.

The third picture shows the cabinet that I am using for now. This cabinet was given to me about 25 years ago by Frank Hilvert. THANK YOU FRANK! I believe it was built by a friend of his family. This unit was built with an outer screen which the amp is sitting on, while the actual speaker cabinet is lying on it's back in this photo.


It turns out that this was a folded horn design by Klipsch, which I located in a loudspeaker desing book from the '50s. This is visible in the forth picture.

3 for 3

My parents were in town this past weekend for another visit. This time my father and I had more time to spend working with three amp projects. First we looked at the Champ 5E1 project that started all of this. We confirmed that I do not have a center tap on my RCA power transformer so my options are to either create an artificial tap and use the 5Y3 for rectification, or create a bridge rectifier using 4 diodes, donated by my neighbor (thanks Bryan!). Next we spent time slowly powering up the Western Electric 124c Dad pulled out of the town dump! This thing was THE workhorse of the early '50s. As you can see in the photo above, this amp has 19" rack mount ears on either end of ths chassis and a full-size face plate that mounts on the bottom which is actually the front. Click on the photos to see larger versions.

The third amp was the Hammond AO-35 which was donated by Ron Ashcroft last year. I installed new tubes which I bought at the Dayton Hamfest in June 2008. These were two Sovtek EL-84, two Svetlana 12AX7, and a NOS Sylvania 5Y3 made in 1975. We slowly powered this up as well, using the variac I bought at the '08 Hamfest. This amp has no gain control pot, so after a little squealling with a microphone, we plugged my Samick Telecaster in using the Switchcraft adapter I bought from Antique Electronic Supply (visible on the right of the chassis). The amp sounds good, but a thorough test of all the parts will likely turn up some leaky caps. A gain pot would also be helpful.

Pulling Parts from the RCA HG-765L

My folks were in for a visit, and after my dad looked at the layout of the TV chassis, he wondered if their wasn't a rectifier tube somewhere in the circuit. If so, this may indicated the needed 5 volts to operate the 5Y3 rectifier tube in the Champ plan. We'll look closer at the tube layout for this console to learn more.