I am an idiot

I meant more that I was trying to for multiple days to get enough power from 1 tube instead of 2

Ah, give me a break. You're too young to be an idiot. Takes
many years of cultivation before you can lay claim to that
distinguished title.
The card carrying Bob

Tubes!?....I thought I was the only one still using decades old technology! My vehicles all have carburetors!

yea tubes
I love them
and currently I have 2 amps
and made my sister one
all work great (I can post some pics if people want it)

robot797, I wouldn't be so hard on yourself if I were you. Things happen in this imperfect world of man-made products. During troubleshooting, you found a bad output transformer winding. It was not unusual back then, why they had replacements available everywhere, last being Radio Shack before they became a cellphone and gadgets store.

The lacquered armature wire used for transformers, over time the lacquering could break down, something cause them to run hot then insulation fail, or overcurrent happen.

Most common failure with tube stuff back then was electrolytic filter capacitors for power supplies. One would get a loud A.C. hum, which was a sure sign these gone bad. There were usually 2 in the B+ (higher voltage side, cheap stuff had no isolation or step up transformer, straight A.C. to the chassis for common). Common combination was 40 ufd, 20 ufd. I might have to substitue 20 ufd, 20 ufd, which still worked.

It was fun to use 2K Ohm headphones where one only had the pre-amplification stage.

Still remember the Graymark 3 tube shortwave radio kit I built in the late 1960's, used 12AU7 regenerative tuner and audio preamp, 50C6 pentode amplifier, 35W4 diode in power supply. Used plug in coils to change bands from AM Broadcast to 15 meters. I would listen to late night broadcasts from BBC Australia in the wee hours of the night in high school.

Sorry to deviate, brings back a lot of good memories of the old stuff used to do when growing up.

GallopingGhostler wrote: Sorry to deviate, brings back a lot of good memories of the old stuff used to do when growing up.

Everything made sense years ago. Tough to recapture. In a dream here and there
maybe, if you're lucky enough. It's got to happen in your mind. Hopefully in high defination.
Melancholy Bob

dckrsn wrote:Everything made sense years ago. Tough to recapture. In a dream here and there maybe, if you're lucky enough. It's got to happen in your mind. Hopefully in high definition. Melancholy Bob

Bob, unfortunately, these days it seems kids can't be kids any more.

I sometimes think that nowadays, one would be better off bringing up their kids in a 3rd world country where they are still allowed to use their imagination and kids can play with others without having a heavy handed state after their parents for not not supervising them. Or, to live rural on a farm.

I even remember when low cost home computers came out in the 1980's. It was a time of discovery, kids and adults learned to program in BASIC language, it taught them math and logic skills, thinking, creativity. It was short lived, forces beyond us shifted us to canned stuff that supposedly did more, but we learned less. I abhor the modern conveniences of so called thermostats, Google, Amazon, you-name-it intelligent talk to devices.

Of all the crazy things, an adolescent built a kit digital clock and brought it to school one day for show and tell may be 15 years ago, was arrested for creating a device that could potentially be a timer for a bomb. He happened to be of Arabic descent, parents legal immigrants to US. But I digress, seems all of common sense has slowly been leaving us.

Still got my aftermarket CB radio installation to do to my 2001 Kawasaki ZG1200 Voyager XII to do. Got most of the stuff, just need to find the time.





Sorry, still off topic, but a project I've been wanting to complete to add aftermarket CB to the factory Clarion radio on my tourer.

Robot, I think I know what you mean. It has happened to me a couple of times, don’t know if you should give an ”attaboy” pat on your own shoulder or kick your own butt after spending a couple of days troubleshooting a mystery that turns out to be the most obvious failure. Not that a faulty output transformer would be an obvious failure to me at all The fact that often this kind of mysteries are solved in 3 seconds by a person that just happens to walk by, does not help with the feeling either

I like tube amps too, I only have one, built from a kit as I don’t have the skill nor knowledge to design my own. But I like to build. I know the principles of their operation but trying to apply that in practice would likely result in foul language, smoke and possibly an electricution

KariFS wrote:I like tube amps too, I only have one, built from a kit as I don’t have the skill nor knowledge to design my own. But I like to build. I know the principles of their operation but trying to apply that in practice would likely result in foul language, smoke and possibly an electricution

Kari, regarding design knowledge, the ARRL (American Amateur Radio League) used to (I don't know about now) carry for sale their handbook. It contained information on electronic theory, in an easy to assimilate style of writing, for amateurs to gain enough electronics knowledge to build their own equipment and pass the Federal Communications Commission (FCC) tests to get their amateur radio operator licenses. If you had such a book, I believe you'd amaze yourself on what you could do.

Much in life is not so much how much you know, versus where to find the information and make use of it.

I find digital circuit design much easier to do. The simplest digital circuit is a transistor with current set to full saturation (i.e., 100% amplification). Doing a little reading from a few books I have on digital electronics, in the mid 1980's I made a very small adapter board tubing shrink wrapped to the home made cable from my Radio Shack CoCo (color computer) 2 (AKA Tandy in EU), using one transistor and 2 resistors. (I think it was a PNP, but so long ago can't remember details unless I redo.) Back then, printers were very expensive, so one benefited from surplus used equipment. One catch with this inexpensive narrow thermal paper printer (think it was 6" wide) is that one of the signals, I think it was to latch the printer was inverted. (Voltage was +5 when it needed to be 0, and vice versa).

By using a single transistor and some resistors, I was able to make a simple inverter or NOT gate. Connected printer through a custom cable made of ribbon cable to the printer, and it worked!

Having the correct references (and these days, books are cheap on the used market) really helps one along. You don't have to be an electrical engineer or seasoned electrician technician to do circuit design.

(again   ) One of the reasons why I changed college majors from electrical engineering to mechanical junior year was purely theoretical stuff that I found hard, such as imaginary numbers. Electrical engineers do imaginary numbers and I guess talk to imaginary people. Yet my first job after graduating was an electrical engineering position at McDonnell Douglas. As I go promoted through various positions, ended up retiring from the government while in a civil engineering position.

I guess there isn't much difference between electrical circuit analysis and concrete slump calculations.

I still think the easiest to learn are tubes
I can make a simple 5W amp with only 10 parts (excluding power supply)


but I also have good news
my (2 months back) ordered transformers are in europe so delivery might be soon
and I might have found a set of universal transformers

Like my Dad use to tell me ( when i did a repair on something of ours that was a PIA ) at least you can fix it yourself and that was the response i gave him then , now i see the difference when you take to a repair shop get it back and still is not right after paying Big $$$ to fix . Glsd you got it fixed . Sure we want to see your other amps !! I have a 100W fender reverb guitar amp w/tubes it will blast ur head off !!

GallopingGhostler wrote:
Much in life is not so much how much you know, versus where to find the information and make use of it.

Very true in many aspects of life. In retrospect, I may have been able to design and build my own amplifier, but it was easier to learn the principles first by building one from a kit. Cheaper too. Assembling the kit only took maybe a couple of weeks worth of evenings, I made sure that if at all I didn’t ”feel like it”, or if I felt tired, I called it a day. After all, there are voltages in excess of 360VDC in there, another reason to not experiment myself with the design, and to make sure I was concentrating on what I was doing.

Below is the schematic for one channel (power source, heating and signal source selector excluded). Quite a simple design with not a lot of components, but the capacitors and the feedback loop are a bit of a mystery to me. I sort of understand their purpose and function, but how to select the correct values for each... Designing my own would have taken months of research and experiments, and before building this one I was not sure even from where to start

okey lets see you can cut out a lots of parts without changing the funktion
also change the tube same power but single enphelope
the feedback is just wrong
so so so wrong
also feedback is optional

this is a fast edit of what I would do
also I would use a ecl86 or pcl86 instead of a ecc81 and el84

The amp in question is meant for general Hi-Fi use, and I guess the R2 and R6 are there to ”play it safe”, to keep the input signal to the valves in a safe level? But that is just a guess, what do you think?

R9 is parallel to the secondary of the output transformer. It is there to protect the transformer, because an open circuit could damage it. It is very easy to create an open circuit as there is the mute switch (that you also deleted ), I know I would have fried a couple of those transformers already The mute switch is there to accommodate the use of headphones. A practical thing, not essential obviously.

The feedback circuit is there to reduce distortion (the output transformers are cheap quitar amp units) and also to make the amp less sensitive to the changes in the speakers’ impedance. This is what I read in the magazine article about this amp. Again, this amp is for beginners, and supposed to work with many kinds of speakers, so the design needs to be ”robust” rather than optimized for max power.

The tubes were selected based on the price and availability, both the EL84 and ECC81 are currently manufactured and inexpensive. A pair of matched TAD EL84’s was 34€, and the ECC83’s start at 15€. The Genalex ECC83 I got was 42€, but that’s supposed to be one of the better tubes. Unfortunately the one I received is faulty, so now I am running the 15€ JJ that came with the kit. Anyway, having separate tubes for pre- and power stages makes it possible to affect the sound by changing either pre or power tubes or both. That and cheap, widely available tube types make it interesting

It would be interesting to know more about the feedback thing, and why do you not like it. As I said before, I am a beginner with electronics, keen to learn more.

you know a pcl86 witch is a 1/2 ecc82 and a el84 in one tube costs new around 4 or 5 euro
I have like 50 or 100 just lying around

r9 is part of the feedback circuit
and a protection for the mute switch
a output transformer must be shorted when there is no speaker is connected
the feedback is a humm and distortion reduction
if you build the amp correctly you dont need it and you will get more output power (yes feedback reduces output power)
and if I add feedback I always add it with 1 resistor from the 8ohm line to a dual resistor circuit on the preamp tube


here have 4 pics of the tube amps I have build over the last 10 years
(and the prototypes and failed ones I dont count)