DIY Guitar & Amp

Champ amp now in cabinet

2012-01-27T11:38:00.005-05:00

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

2011-11-27T09:27:00.010-05:00

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

2011-03-03T21:30:00.005-05:00

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

2010-06-19T14:10:00.009-04:00

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

2010-02-17T19:13:00.005-05:00

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

2010-01-28T19:02:00.004-05:00

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!

2009-12-26T10:35:00.014-05:00

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

2009-11-16T20:58:00.004-05:00

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

2009-07-06T05:28:00.002-04:00

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.

Tektronix Oscilloscope for Parts & Variac Made Functional

2009-05-05T20:45:00.004-04:00

Another Craigslist freebie! The Tektronix Oscilloscope seen here is a vacum-powered tube unit from probably the mid-60s. (click the photo to enlarge) I hope to pull various components off of this. I had the opportunity to spend a couple of hours rewiring the Variac I bought at the Dayton Hamvention last year. My Dad told me I may be able to rewire the coaxially mounted M5 variable transformers, from 3-phase 240vac to 120vac. I did this and the test I performed afterwards is in the video below.

Console #4: RCA HG-765L

2009-04-11T13:53:00.005-04:00

This unit was likely made in the mid to late '60s. Paula is overjoyed that yet another old console will sit in the garage while I strip it. This is another Craigslist freebie. What I am likely to do with this is pull the TV chassis out, along with some other very small pieces, and dump the rest. Though the TV chassis is tube, the audio component is solid state. This is the same configuration that I found in the Magnavox that I got at the very beginning of this project. Yes the Pavarotti LPs came with it. THANK YOU BRIAN FOR YOUR HELP GETTING HOME!

Inside the Variac

2009-04-05T14:56:00.005-04:00

I haven't touched the amp project in nearly a year. I have acquired additional test equipment though, to include a an a capacitance decade box, capacitance analyzer, a bridging transformer for impedence mathing in audio inputs, an RF Signal Generator, a DC ampmeter, and an older multimeter. But of course the hard part has been finding time to put this stuff to good use. I did pull out the Variac that I bought last year, with the goal of getting it into action. I will need it to safely test amps and individual components like transformers. For starters I cut the wires off, and removed the cover. I have obtained enough technical information about this that I hope to get it wired for 120vac-to-120vac use soon. But not without a call my pop first. Please click on the photos here to see enlarged versions.

Oscilloscope arrives!

2009-01-12T22:09:00.005-05:00

I haven't touched the amp project since getting parts at the Hamvention early last summer. I hope to spend some time on it over the next few months though. Today I finally got my hands on an oscilloscope. Thank you Mike! It is a B&K Precision Model 1461. I am not sure how old it is but I would bet 15-20 years. It appears to be in nice shape. I don't know much about these so I will have to do some reading before I even turn it on. One sour note, B&K Precision doesn't provide support directly for their older equipment. They transferred the rights to the technical documents, to a subsidiary. This company wants $25, plus shipping, for the 35 page owner's manual! I may end up spending the money though.

Hamvention 2008 - Dayton, Ohio

2008-05-18T07:25:00.009-04:00

The only other time I've been to the Hamvention (or Hamfest) was about 30 years ago. It is still big. Way too big to be taken in thoroughly in one day. Tickets at the door were a steep $25 but that is good for all three days, inside and out. It really is targeted at amateur radio folks, but all kinds of electronics are available in the flea market. Of course my interest was in parts for the Fender Champ 5E1 I am building, as well as tubes for the Hammond AO-35 that I just acquired. In that department I got the following: EL84(2), 12AX7(2), 5Y3(2), 12AT7(1), 6V6GT(1). Two are used, the rest are new. I paid an average of $7 per. New tubes like this would run me $12 and up not including shipping. I also got I handfull of high-voltage caps, four tube sockets, and some IEC 320 sockets (for AC power cables). I found a turret board with capacitors and large pilot lights attaced for $2, and a pile of selenium rectifiers for $5. The best, and least expected, deal of the day was the 3-phase VARIAC I found on the way out of the show which I paid $20 for. I hope to use this to slowly power up amps when testing. Since the flea market is so large, some folks use wagons or backpacks to tote stuff around. I met a guy who had the gest solution I've seen. He built a cart from angle iron, which holds milk crates and coolers, with two PVC tubes in the back for antennas. He actually mounted a spare wheel and tire underneath in wagon, just like a truck. You can see this in the photo at the bottom of this post. Remember to go to my actual blog and click on the photo thumbnails to open larger photos.

Organ Amp #1: Chassis AO-35 from a model M100

2008-05-12T20:42:00.006-04:00

My co-worker Ron Ashcroft has graciously donated this reverb amplifier from his old Hammond M100. The unit is designed to take a signal from the driven reverb, sending it through an ECC83, a 12AX7 which splits the signal to drive two 6BQ5 (EL84). The bottom image is a schematic.

Console #3: Olympic Model 1770

2008-04-26T10:16:00.003-04:00

This is a tube fired AM/FM turntable stereo console made in the early to mid '60s. The original purchaser/owner of this was asking $20. It likely has some parts I could use, so even though it didn't power up I actually paid $10 because there was an obvious sentimental attachment for the owner. It appears to be a cheaply built, in Great Britain I believe. The turntable is marked BSR. The circuit arrangement is rather curious. The lower image below shows the tube configuration. It appears that the preamp chassis is separate. Another oddity is the lack of power transformer.

Console #2: RCA VHT-46

2008-04-23T23:36:00.001-04:00

This was another free listing in Craigslist. It is solid state console produced in that late '60s. I don't yet know what parts from this will be useful for my amp.

Tube testor works...I guess.

2008-04-13T19:26:00.000-04:00

I bought this tube tester last year, probably before I retrieved the Magnovox console. This Century model FS-2 was made in the late '50s or early '60s. I hadn't tested it or tried to use until today. There were NO diagnostics or self-test described in the manual, so I had no real way of knowing if it works. I read the instructions and plugged it in. No sparks or explosions. I tested the REALISTIC brand 12AX7 which I pulled from the Magnovox, as well as a 5Y3 and three 6L6GT tubes which were in a batch of (over 100) tubes that came with the testor. The 5Y3 is a CROSLEY brand and it tested fine. But only one of the 6L6GT tubes tested OK and it is a SHELDON. Also visible in these photos are the two cold-war era Polish ammunition cans which will serve as a chassis for this project and possibly for my tremelo and reverb unit too. I have choke transformers also, so the only major component that I am still missing is an output transformer.

The power transformer works!

2008-04-07T23:46:00.000-04:00

And I have a scorched test lead clip to prove it. Though a poor choice of conections roasted a test lead, there was no fire and the transformer wasn't damaged. This transformer produces 320VAC and 6.2VAC, but it since there is no HV center tap I will need to use a modified rectifier circuit.

Console #1: 1969 Magnavox Astrosonic Console

2008-04-06T07:26:00.000-04:00

In the fall of 2007 I decided I wanted to build a tube guitar amplifier. Since my "all-scrap" playhouse project worked well, I decided to try and build the amp from scrounged parts only. I got lucky when I came across a free ad in the local Craigslist, for this old TV console. The TV section was all tube so I tore the whole thing appart. From this I retrieved a pair of HF horns, a pair of 15" LF drivers (and cross-overs), several vacum tubes, and four transformers, along with a bucket of hardware.