The Voodoo Doctor

I have some experience with the solid state rectifier replacements. Typically they are just a couple of diodes and a series resistor. They only simulate the diodes and series resistance of a tube rectifier. This is a pretty good simulation of a tube rectifier, but they do not provide a slow start up for the B+ voltage like a tube rectifier. So if you do not have a standby switch or time delay circuitry on the B+ line, these are not a good alternative. If you do, go ahead and use them. You will notice no difference in performance. CSB

Triode Electronics is a good place. I used to go by there when I used to live/work near Chicago. Their shop probably looks a lot like some of our garages, but they knew where everything was. Lots of cool stuff, and good people to do business with. I haven't bought any NOS tubes in a while. I came across a good stash a few years ago, and got a stupid good price on them (including some old Mullard KT66's). I used to work with a guy that helped clear out the old RCA tube plant when it closed down. He had tons of old tubes packed away in the bulk packaging. His garage was just filled with thousands of old RCA tubes. Well, it sounds like you have the hook-up and know the right people. Keep the valves a burn'in, CSB

For the ST-70, the schematic (with EF86's) can be found on the Triode Electronics website. See link below. http://www.triodeel.com/dyna1.gif http://store.triodestore.com/dynacoupgrades.html They also have a decent amount of information amount Dynaco ST 70's and possible upgrades to the amp. So if you are a "do-it-yourself'er" this is a good place to look for additional information and popular upgrades. CSB

Using a 5Y3, your B+ voltage to the output tubes probably drop around 40V DC more compared to the GZ34. (This is assuming about 140mA at idle from the B+ Plate supply.) The amp is rated at around 16 Watts per channel as designed (w/ GZ34). So you are probably only losing a watt or two when using the 5Y3. With that said, you will be hard pressed to hear any difference when operating within the normal region of the amplifier.<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" /> If you are really pushing the amplifier, so you get some compression on the transients, that is where you may hear some difference. - To try and hear a difference, start with the GZ34 in the circuit. Turn the amp up to the point where you just start to hear the compression/distortion. Then turn it down just a tad to the point where the amp sounds clean again. - Now, leaving your levels the same, turn off the amp, let it cool down, and then swap out the GZ34 for the 5Y3. Turn the amp back on, and give it a listen. For Hi-Fi amps, you will probably never hear a real difference during normal operating conditions (with a self bias/cathode bias circuit). When dealing with guitar amps, etc... where their normal operating conditions are pushing the amps well into the non-linear region, and you actually send the output tubes into saturation, the difference between rectifier tubes can be fairly obvious. Also, is you are running a fixed or adjustable biased amp, the drop in B+ voltage may require you to re-bias the output tubes. Before the re-bias, you may be running the tubes colder (less bias current) than before. In this case, you may be able to hear an increase in distortion. But once the tubes are biased properly, there will probably no audible difference between rectifier tubes. For replacement tubes, you may have a hard time finding anything other than Groove Tubes in Indy. You might find some Fender or Mesa branded tubes too. I have always ordered new tubes online. I have had good luck with Triode Electronics (http://www.triodeelectronics.com/), Tube depot (http://www.tubedepot.com), and Antique Electronic Supply (http://www.tubedepot.com). Around $14 for a JJ 5AR4. Kevin Silva at Uncle Alberts may carry a variety of tubes, but I'm not sure about that. CSB

You may also want to be careful when buying Mullard branded tubes, unless you know exactly what you're buying. The Mullard brand was recently purchased by New Sensor (Sovtek). So a "new" Mullard may be made on the same assembly line as that Sovtek you are replacing. Sorta takes the cool factor out of the Mullard brand. But I think they are only currently manufacturing EL34's, EL84's, and 12AX7's. So if you are buying Mullards, buy from a well respected vendor. CSB

Check the post below for a little more information on how a rectifier could effect your sound. But since these are the same tube types, I wouldn't expect any sonic differences. http://forums.klipsch.com/forums/thread/962954.aspx The Dynaco ST-70 also uses a inductive input filter after the rectifier. This inductor will try to keep the current flowing through it as constant as possible. This will even further decrease the sonic differences between different rectifier tubes by 1) helping regulate current flow through the power supply and 2) decrease the rectifier tube's effect on the overall power supply impedance. Unless you are noticing a difference in performance, there is probably no need to replace the current rectifier. CSBhttp://forums.klipsch.com/forums/thread/962954.aspx'>

In most situations, you can replace a 5AR4/GZ34 with the 5Y3 since they have the same pin outs. From what I can find on the Heathkit AA-111, you will be fine with using either tube. But these tubes do have different ratings, so it is always best to use caution when swapping rectifier tubes. Things you will have to consider are: - Difference in DC output current ratings - Difference in allowable filter capacitance - Difference in Plate Resistance - Difference in Heater current ratings There are also differences in the performance of the two tubes. The primary difference that you may hear is due to the internal plate resistance. The 5AR4/GZ34 has a total plate resistance of approximately 80 Ohms when used as a full wave rectifier (two plates in parallel). For the 5Y3, this resistance is around 400 Ohms. So when you are pulling significant current, you will get much more voltage drop across a 5Y3 compared to a 5AR4/GZ34. This will result in lower plate voltage and lower total output power. This is why the 5AR4/GZ34 would be better at low AC Mains voltages. For a Class A/B amplifier (which I believe is the case with the Heathkit AA-111), you may actually be able to hear a difference between the two types of rectifiers because the plate currents vary depending on how hard you are pushing the tubes. This will give you a compression effect, since there will be more voltage drop during loud signals, than during low level signals. This compression will be much stronger using the 5Y3. This gives you what some people refer to as "bloom" during some of the notes. The voltage will drop during the initial attack, but then the plate voltage will rise once the signal level begins to trail off and the plate current decreases. For looking at tube technical specifications, www.duncanamps.com is a great place to start. Their Tube Data Sheet Locator is a great source to tube datasheets. It also provides a list of substitutes for these tubes, which may or may not be useful. Hope this helps, CSB