Stereo 35 output Vrms?

[sbelyo]

I haven't logged on in a while so I'll start by saying that I only finished half of my stereo 35 rev c. I have mainly switch to headphone listening so that the reason for the incompletion.

I am looking to use the stereo 35 for the akg k1000's

Their manual says to connect it directly to the speaker outputs of an amplifier.

I know they require 7 Volts rms

They have 120 Ohm resistance

Power Rating is 1 watt

I remember that the stereo 35 is 17.5 watts per channel. Other than that I am not certain how the rest relates?

Any Ideas?

[mesherm]

If it was me, I would wire an 8-10 ohm 20 watt resistor across each output channel and THEN connect my headphones so that they parallel the 20 watt resistors. That way the output transformers are properly loaded. The combined resistance of 120 ohms and 8 ohms in parallel is only about 7.5 ohms. Well within the impedance range of most 8 ohm loudspeakers.
It is usually not a good idea to run a tube amp with the output transformers unloaded. At full rated power with the resistors in place the voltage across your headphones will be 11-12 volts. But I doubt you would ever run the volume that high.

[Shannon Parks]

If it was me, I would wire an 8-10 ohm 20 watt resistor across each output channel and THEN connect my headphones so that they parallel the 20 watt resistors. That way the output transformers are properly loaded. The combined resistance of 120 ohms and 8 ohms in parallel is only about 7.5 ohms. Well within the impedance range of most 8 ohm loudspeakers.
It is usually not a good idea to run a tube amp with the output transformers unloaded. At full rated power with the resistors in place the voltage across your headphones will be 11-12 volts. But I doubt you would ever run the volume that high.

Though I've never done it, I concur with Mesherm.

Any stable amp should be OK without a load and without an input. Tube amp owners have done this a million times without damaging their amp, though it's probably not recommended - since that yard sale pickup might just be an oscillator. Running an amp without a load and with a source (or an unstable amp, like your yard sale find) will be what causes problems. The output sees an infinite output resistance and creates very high voltage on the primary. I'd guess this would probably damage the power supply, perhaps the diodes then blow a fuse, before it damaged the output transformer.

Shannon

[sbelyo]

Thanks I'll give it a try....

I just wanted to see if I needed to buy different iron before I took the plunge and bought some.

What's the Iron everyone is using these days?

[EWBrown]

This one from Triode Electronics, is an excellent new production copy of the original Dynaco Z-565.

http://store.yahoo.com/triodeel/z517wadyoutr.html

It is different in that the secondary is 4 and 8 ohms, not 8 and 16.

Hammond 1650F is frequently used, as are original Dynaco Z565s salvaged from SCA35s or original ST35s.
Magnequest makes a real nice (and expensive) Z565 replacement.

/ed B in NH

[mesherm]

I've used the Triode Z-565s in one amp and an original set of Z-565 trannys from an SCA-35. Both sounded great. SCA-35s usually go for less than the ST-35s on Ebay.

[EWBrown]

A more conventional method to run headphones from an amp, is to connect a 8 ohm (at least) 10 watt resistor across each output, (use 16 ohm resistors if you choose to use the 16 ohms output). Then connect a 120 ohm 1/2 or 1 watt resistor from each "hot" speaker output to the "sleeve" and "tip" connectors, respectively, on the headphone jack, and the "ring" of the jack (or ground) to one of the speaker output grounds.

The whole idea is to not feed the amp's output directly into the 'phones, this can cause blown phones (and eardrums), especially if listening to some of the TelArc recordings with Digital Cannons or Thunderstorms.

On a 3 conductor phone plug, the convention is that the tip is called "tip", the middle portion is called "sleeve" and the ground/common is called "ring". Old military and TelCo lingo, here...

/ed B in NH

[Shannon Parks]

A more conventional method to run headphones from an amp, is to connect a 8 ohm (at least) 10 watt resistor across each output, (use 16 ohm resistors if you choose to use the 16 ohms output). Then connect a 120 ohm 1/2 or 1 watt resistor from each "hot" speaker output to the "sleeve" and "tip" connectors, respectively, on the headphone jack, and the "ring" of the jack (or ground) to one of the speaker output grounds.

Hi Ed,

Have you ever made a headphone amp before? I'm trying to wade through all the DIY stuff out there to determine what makes a good headphone amp (ie overall gain, output Z, etc.). Also, does anyone swear by OTL headphone amps? Just some ignorant questions. I need to go buy some AKG 'sonar quality' cans. Yellow_Light_Colorz_PDT_19

There's gotta be a way to get the Ipod generation hooked on tubes. Apple already has them hooked on stereo - a good thing, IMHO. Maybe I should head over to www.headwize.com.

Shannon

[EWBrown]

I have built the BottleHead "SEX" amp, uses 6DN7 spud tubes as a 2WPC SET amp. It is also set up as a headphone amp, the phone jack is the standard 1/4 in dia 3 conductor type. The 8 ohm speaker outputs are connected through 120 ohm 1/2 watt resistor for each channel. It sounds great with Sennheiser HD-600s! Itr is a good idea to load the 8 ohm speaker outputs with 8 or 10 ohm 2W resistors.
This 120 ohm resistors-in-series method is pretty much of an industry standard, for feeding phones with a power amp. This works well with 'phones between 32 and 300 ohms impedance. If anything this helps to preserve one's hearing...

I've seen the HeadWize site, and have printed out the schematics and parts list. I'm planning eventually to build one up, using a 6080 rather than a 6AS7 (identical specs) just because I have several 6080s, and only one 6AS7, and that one is rather "questionable" shape.

I've played around with LM380 and 386 IC headphone amps in the past, and was really underwhelmend by their poor sound... Tubes are the way to go.

After listening through $15 CD player grade 'phones, the Senns are a real awakening! Antique Sound Labs and others have latched onto the tube headphone amp market already, their units sell between $400 and 800, for relatively simple circuitry. The fancier ones have a line stage and 3 or 4 source selector switch.

/ed B in NH