low output

[VictoriaGuy]

I'm using Hammond 125Ds. The data sheet says The OT secondaries go right to the speakers using 2 of 6 lugs to match the appropriate primary impedance.

I understand now.
That's one of the 'universal' OTs from Hammond. In transformers, the impedance can be thought of as being 'reflected' across the windings, so for an OT the tube will 'see' a different impedance depending on the speaker impedance connected to the secondary. The Hammond datasheet provides info on which terminals to use with your speaker to 'reflect' the proper impedance back to the tube (primary) side.

The schematic is for a different OT that says it has a black wire going to ground... (the Hammond doesn't have this).

So I wired the Hammond right to the speakers and got a better result.

With that circuit, I don't think it should make a huge difference either way. What difference did you find (with one side of the speaker gronded)?

I don't know for sure that the other OT is bad, but I'm waiting for my oscilloscope leads and I can't find any errors on that channel...yet. I suspect I might have ran it without a load or shorted it. I have found some troubleshooting data to check resistances across the primaries as a quick diagnostic. They both have the same values so maybe it is good.

It's not that easy to 'fry' an OT, so you can keep checking for wiring problems- make sure you don't have a short across the speaker terminals, etc..

 

[fleapower]

aah so reflected across windings since the we're not dealing with two things that touch directly? I have picked up some bad slang.

I'm pretty satisfied with the accuracy of the wiring so far. The only problems have been whoppers and look ridiculous in hind sight.

I've switched inputs, swapped speakers left to right and generally looked at everything ... everything as suspect. I even took the whole set of tubes and swapped them back and forth. It's really just a matter of time.

 

[VictoriaGuy]

aah so reflected across windings since the we're not dealing with two things that touch directly?

Correct- think of a transformer as a 'ratio machine'...
It's the turns ratio of the primary and secondary that matters.

BTW, since most speakers are 'all over the place' with impedance varying with frequency, the whole impedance matching process is a bit approximate...so don't worry too much about it when you are just trying to get your amp working.

 

[rcollege]

For audio, almost any insulation is fine provided it can handle the voltage and the heat - and even this does not matter if the wire is stiff and not touching anything.

Best to use a colour scheme to aid fault-finding. This probably requires PVC insulation - which is fine.

I have found magnet wire in 4 different colors now. Temco has a good selection of amber, green and red. Plus they have motor run caps...along with some transformers.

https://www.temcoindustrial.com/shop/wire-cable-accessories/magnet-wire.html

I found burgandy magnet wire at another electronic supply store. Also, I will use different gauge sizes...such as thinner wires for grid 1 input wires.
I'm using twisted amber and red for the heater wires.

PVC is fine... just finding solid in gauges less than 16ga and higher than 600V is difficult.

Longevity is a concern for me as well- I want my great, great grandchildren to enjoy the amps I make. Magnet wire doesn't seem to degrade much.

 

[fleapower]

Well I thought i'd check in ... My Musical Machine is working almost perfectly. Slight 60 Hz Buzz that may be due to my non-twisted heater circuit. It'll go on the scope this weekend for measurements. I saw the heater how-to a little too late to fix it. The culprit for the quiet audio was......long speaker wire across the posts. Yes, embarrassing.

The plan is to make a second one for son #2 and make a cool chassis x2. I want it open to measure, record and maybe swap in the power circuits individually that we made as 3 distinct parts. I doubled up on a lot of the cheaper parts when ordering so we have a lot to start with. The learning part is awesome too. Incredibly gratifying, too.

I do have on question ... how can you get that sound out of ~8 watts? I really did not expect the loudness. I had unrealistically high hopes for the sound quality as well that were also exceeded.

So overall we're thrilled. But chomping at the bit to make another and improving.


Thanks, all

 

[VictoriaGuy]

Slight 60 Hz Buzz that may be due to my non-twisted heater circuit. ..... I saw the heater how-to a little too late to fix it.

It's called a soldering iron, but it works to unsolder also!
Never too late to make things right - you can always extend wires with solder joints and heat-shrink insulation, or adding a terminal/lug strip as connection point.

The plan is to make a second one for son #2 and make a cool chassis x2.

Copying Pointz' chassis design - with the PS on one side and the amp on the other - could fit with your plans to make things 'modular'. It worked for me.

 

[stocktrader200]

iPhone puts out about 1 v . I needed a 6db ( 2x ) amp to match the other inputs on pioneer sx 3700. If you boost the bottom end an additional 3 db, it sounds as good as any CD player with lossless files.

 

[fleapower]

It's called a soldering iron, but it works to unsolder also!
Never too late to make things right - you can always extend wires with solder joints and heat-shrink insulation, or adding a terminal/lug strip as connection point.


Copying Pointz' chassis design - with the PS on one side and the amp on the other - could fit with your plans to make things 'modular'. It worked for me.

I hear you! I love Pointz's design, so I'll probably keep the same general layout but boy the things you learn on your first go-around. The clumsy layout issues look so simple in hind sight.