I Like Ike

[Shannon Parks]

OK, the Eiclones (pronounced Eye-clone, derived from Eico & clone) are humming along. I just need to get a few hours in a real environment under their belt with some real tough ribbon speakers.

I had a neat learning experience studying up on stability networks, and I will have to recommend Rozenblit's book Beginner's Guide to Tube Amp Design. The gain and NFB numbers just don't seem to add up in the Eico HF-87 and the Dyna MK III manuals. The Ike's open loop gain was almost beyond my measuring capability as my signal source output sucks below 20mV, so I removed the 12AX7 cathode bypass cap to simmer things down (ie a little local NFB). At this point, I'm extremely happy with the results - the testing numbers are there. The Hammond transformers have performed beautifully (1650Ns). Maybe not Acrosound specs, but very repectable, and MUCH cheaper. But real world listening tests are next, and the most important.

Shannon

[nineno]

At this point, I'm extremely happy with the results - the testing numbers are there. The Hammond transformers have performed beautifully (1650Ns). Maybe not Acrosound specs, but very repectable, and MUCH cheaper. But real world listening tests are next, and the most important.

Shannon (et al), I think you commented on this topic in the ST-35 forum earlier, but I wanted to sort-of bring it over here where it may apply more.

You're currently using the 1650Ns with the BigBlue, apparently. One of the potted trannies from Hammond would work, as well?
http://www.hammondmfg.com/1650p.htm
If i had to guess, i would assume the 1650KP (3400ct & 318ma). Is that correct?

I'm sure the other ones might also be applicable depending on which "flavor" of BigBlue you build, too?

I might have to go hog-wild and get a torriod power transformer and a potted output. 8)

Does anyone have any comments towards potted and toriodal transformers as aposed to standard irons?

drew*

[Shannon Parks]

At this point, I'm extremely happy with the results - the testing numbers are there. The Hammond transformers have performed beautifully (1650Ns). Maybe not Acrosound specs, but very repectable, and MUCH cheaper. But real world listening tests are next, and the most important.

Shannon (et al), I think you commented on this topic in the ST-35 forum earlier, but I wanted to sort-of bring it over here where it may apply more.

You're currently using the 1650Ns with the BigBlue, apparently. One of the potted trannies from Hammond would work, as well?
http://www.hammondmfg.com/1650p.htm
If i had to guess, i would assume the 1650KP (3400ct & 318ma). Is that correct?

I'm sure the other ones might also be applicable depending on which "flavor" of BigBlue you build, too?

I might have to go hog-wild and get a torriod power transformer and a potted output. 8)

Does anyone have any comments towards potted and toriodal transformers as aposed to standard irons?

drew*

Good comments. The potted outputs and even the 37X series of PTs give us so many options from Hammond alone. All three of these potted models would work, but 3.4K impedance is getting low, but might fine for the 6550/KT88s. The Acro TO-330s in the Eico HF-60 were 3.9K, which is kinda low. Actually, the 5K model would be my first choice and the 6.6K next - but only if I didn't want to use 6550/KT88s. If you ever wanted to mess with pseudo-trioding the higher impedance would be beneficial, too (I would think).

I have the toroid from Maryland on it's way for use in a stereo unit and another standard one from Angela coming. I'll do a shootout in the lab. The regulation of the Hammond 274BX ain't shabby, as far as I'm concerned. Heat and size will be interesting, though, compared to the toroid. As far as potted trannies, I will defer to others more knowledgable. LeFevre had a neat article in Sound Practices ten years ago about potting. I sure wish it could be reprinted. I don't doubt the Hammond ones are a great value, though.

Shannon

[nineno]

I have the toroid from Maryland on it's way for use in a stereo unit and another standard one from Angela coming. I'll do a shootout in the lab. The regulation of the Hammond 274BX ain't shabby, as far as I'm concerned. Heat and size will be interesting, though, compared to the toroid. As far as potted trannies, I will defer to others more knowledgable. LeFevre had a neat article in Sound Practices ten years ago about potting. I sure wish it could be reprinted. I don't doubt the Hammond ones are a great value, though.

Shannon

I'll be waiting with baited breath, so to speak.

I originally thought that potting a transformer was just an additional sheild and a way to damp out any mechanical noise (60Hz humm) induced by the caps (bells) buzzing.

I noticed the PT on my ST-35 buzzzzing a bit. I might try to crank down on the screws a little later this weeks once finals are over.

Is this the only "technical" explaination for potting, or is there more to this?

Also, I have two HUGE chokes. I'm not even sure if they're chokes, but it's a big (6in tall, by 4in wide, by 4in thick) deep drawn steel shell with two wires sticking out. The entire thing is FILLED with potting epoxy. They have serial numbers on them, as well. How do i measure these fellas to see what they can be used for? If anyone needs such a device, let me know.

There's a big potted transformer from the same device as the chokes, as well. How to i figure out what the ratings on this stuff is? I know i can measure the resistances, but what about CT and all that jazz?

Back to transformers 101 for me!

drew*

[Shannon Parks]

I noticed the PT on my ST-35 buzzzzing a bit. I might try to crank down on the screws a little later this weeks once finals are over.

Is this the only "technical" explaination for potting, or is there more to this?

I would swag all power trannies probably 'vibrate' at 60Hz (unless your mains is 50Hz :) ) to one degree or another. If it is audible, ie rattling on the chassis, I think your tightening down is the right idea. Maybe you could use some teflon washers or rubber grommets, too. Suggestions anyone? While out in the lab last night, I put my hand on a warmed up (!) PA-774. Though I had never heard a squeak out of it, the vibration was there.

As to how much potting helps, I really need to round up the LeFevre article and sum up it's main points. Maybe I'll email him and see if it's posted anywhere. One point I remember was that potting was NOT a panacea, especially in regards to the old military stuff.

Also, I have two HUGE chokes. I'm not even sure if they're chokes, but it's a big (6in tall, by 4in wide, by 4in thick) deep drawn steel shell with two wires sticking out. The entire thing is FILLED with potting epoxy. They have serial numbers on them, as well. How do i measure these fellas to see what they can be used for? If anyone needs such a device, let me know.

Get an LCR meter. My Wavetek 27XT can check the basic inductance. You have to swag the current capability. I'd save these for a SET project.

There's a big potted transformer from the same device as the chokes, as well. How to i figure out what the ratings on this stuff is? I know i can measure the resistances, but what about CT and all that jazz?

Back to transformers 101 for me!

Ed could probably answer this best and quickly. Basically you use low AC voltages on it to see the turns ratio. What was all this pulled from anyway, another tube amp?

Shannon

[EWBrown]

I have found from past experiences that steel chassis temd to buzz more than aluminum from the stray h-fields from the power trannie, especially when using the horizontal mount (like the Dynaco ST-70). I've tried various methods to silence them, plastic/teflon/rubber washers, making sure that all screws are really tight, and in the case of a "ringing" shell on a HWT power trannie (ST-70 replacement), the top shell had a higher frequency resonance and simply placing a piece of double sided tape on top silenced it. It will work just as well if placed inside the shell, if appearance is important. I stuck a little copper label on the tape, just for cosmetic purposes.

In the case of one old horizontal mount trannie, the thin steel chassis (can you say cake pan?) buzzed rather loudly, I put double sided sticky tape betwen the core and the chassis, then tightened it down, and the buzzzzzzz vanished. THis was for a simple 350-400 VDC and 6.3VAC bench supply, using the NOS 350 VAC/70 mA power trannie that AES has available. These trannies are old, and definitely look old, and of the two I bought, one was somewhat rusty and dirty.

/ed brown in NH

[Shannon Parks]

I have found from past experiences that steel chassis temd to buzz more than aluminum from the stray h-fields from the power trannie, especially when using the horizontal mount (like the Dynaco ST-70).

Interesting. Indeed, the only buzzing transformer I ever had was an old Knight horizontal mounted unit. It made a TON of noise. :redhotevil:

Shannon

[EWBrown]

For quick transformer impedance checks, I use a low AC voltage, 16 VAC
in my case, and feed the primary, and measure the secondary voltage(s).
As impedance (Z) is a square function of the number of turns, the impedance will be (Vout/Vin)^2 times the secondary impedance

For example, if you feed 16 VAC into the "unknown" primary, and get 0.506 VAC on the secondary, the impedance will be 31.62^2 or 1000 times the secondary. assuming an 8 ohm secondary, the primary will be 8000 Ohms.

The potted units with the two leads definitely sound like chokes, if you do a DC resistance reading, be careful not to hold the meter leads to the choke leads with your fingers, this will generate a strong high voltage (low current) flyback and you can get a nasty but harmless jolt.
An easy way to measure the unknown choke's impedance is to once again, use a low AC voltage - I should have mentioned earlier - isolated from the line, using a transformer - and put a known resistance in series with the choke, 1K is a good starting value, measure the voltage across the resistor and across the choke. The reactance of the choke is 2*PI*F*L
in Hz and Henries, for US and Canada, this is 60 Hz, so 2*PI*F works out to 377, So, the reactance of the choke, at 60 Hz, will be 377 X the inductance in Henries. In the case of a 5 henry choke, this works out to 1885 ohms, for the common 1.5 henry Dynaco 70 C-354 choke, this will be 565.5 ohms equivalent.

For those in Europe, Asia and other lands where 50 Hz AC power s the norm, replace 377 with 314 and proceed as above.

So, by considering the choke and resistor as a simple series resistive circuit, the total equivalent resistance at 60 Hz will be 2885 Ohms, the voltage across the inductor will be 16VAC X (1885/2885) or 10.45 volts, and the voltage across the 1K resistor will be 16 VAC X (1000/2885) or 5.55 VAC.

I hope I haven't put everybody to sleep.... :sleeping: :clock: :infinity:

D'OH!!!!!!!!!!!!!!!!!!!!!!

Note: I may not have (hopefully) put everybody else to sleep, but I am asleep... In inductors, E leads I by 90 degrees (and in caps, I leads E), the simple AC voltage measurement of chokes method I just described may be misleading. I'll give it a try in real time and see what I really get for results. YMMV, etc...

Just remember: ELI the ICE man...

/ed B in NH :drinking: :morning: :silly:

[Shannon Parks]

Just remember: ELI the ICE man...

Beautiful morning here - a little foggy but not a snowflake in sight. :)

One general note: Be sure you know which is the primary side before you put 16VAC on it - maybe start lower if you are not sure. If you put this on the secondary by mistake (ie the speaker side) you may have a bunch of HV leads in front of you.

Shannon

[EWBrown]

I usually do a DC resistance check first on any "unknown" transformers and chokes, just to be on the safe side. On OPTs, the primary is always higher DC resistance, however, this does not necessarily apply to power trannies. On OPTs, I typically go plate-to-plate on push pull units, and plate to B+ on SE OPTs (most have only the two connections, some Hammonds have the 40% UL tap even on SE's.).
I found that the 10K primary 25W SE OPTs from HWT were closer to 8K, about 8200 Ohms, as the 16 VAC fed into the primary yielded 0.50 VAC across the 8 ohm secondary (0.35 on 4 ohms, 0.71 on 16 Ohms).

The 16 VAC source I use is aome non-descript 16VAC, 3A power supply that I glommed at a flea market for a buck or two several years ago. One step above a "wall wart". I previously used a Radio Shack 12.6VAC 3Amp trannie, but this 16VAC unit is self contained, and has no exposed 120VAC wiring.

If you happen to have an old fashioned Lionel Electric Trains (AC) transformer, this should also work well, and it has the advantage of varying the voltage and has short circuit and overcurrent protection.


/ed B in NH br-r-r-r-r-r-r-r-r-r-r-r- it's almost 20 degrees at noon

[Shannon Parks]

Good tips, Ed.

Another source would be to rip open any DC wallwart and remove the diodes and cap. When I get a round TUIT, I'll use one of these - preferably one where the case is screwed together.

Shannon

[EWBrown]

The aforementioned 16VAC supply is a "table wart" one of the plastic enclosures that has an AC plug and cord going into it, as well as about a 4 foot long cord coming out of it. It is also easy to open, it has four screws holding it together, and not the usual ultrasonic "welding" that can make these really hard to open without destroying them. I don't know what the supply was intended to power, I presume a set of PC speakers, perhaps.
Brand name is Philips.

I bought two of these, the other is wired up to a home made variable DC regulated supply, using an LM350 regilator and a handful of other parts.

Don't overlook "wall warts" as possible tube filament supplies, they're great for simple small tube devices like preamps, etc, that can be
left powered up all the time. Been there, done that, it works great!

/ed B in NH

[Shannon Parks]

Don't overlook "wall warts" as possible tube filament supplies, they're great for simple small tube devices like preamps, etc, that can be
left powered up all the time. Been there, done that, it works great!

This is a great point! I'd always thought about using them for a preamp, but the low power usage could be left on 24-7. This would be perfect for a little phono preamp using two 12AX7s - like the RCA phono circuit - using a real cheap PCB transformer (small isolation tranny that is voltage doubled) for the B+ and then a wall wart for the heaters. Neat!

Shannon

[EWBrown]

Some of the headphone amps use a wall wart (18-24 VAC) that then feeds
a backwards-wired filament trannie to generate the HV AC and DC inside the small amp. Since we are talking fairly low current in this application, this can be done with good results. It definitely won't fly with any real power output...

The tube filaments are driven from the low voltage AC from the wall wart, this can be direct AC, filaments in series, or it can be rectified and regulated for lower noise levels.

THis should be OK for any linestages or preamps as well, with savings on the cost of pricey power iron.

/ed brown in NH