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GZ34/5AR4 vs 5Y3GT rectifier tube replacements?


HarryO

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My anthem has originally had a 5AR4 but came with a JAN 5Y3GT in the power supply. However the manual states" this tube (the 5AR4) may be replaced with the 5Y3 rectifier tube; but note, a difference in performance may be heard, the 5AR4 performs better than the 5Y3 when operating voltage is low".

Some maintain they can hear a difference between various 5AR4's and some say there is no difference only improved longevity with a Mullard. Since NOS Mullards sell for $80 and up, IMO if I swapped out a 5AR4 for a 5Y3, or simply replaced a 5AR4, I'd probably buy a Russian tube first before laying out that kind of dough.

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Speaking of the 5AR4, mine just went in my Dynaco ST-70. What is the best replacement? I am thinking of a Mullard. Any suggestions? Does anyone have an extra to sell to this forum member, because I would rather deal here than eBay!

Thanks!

Andy

I do not have an extra one, but here's my .02 worth. I've always heard that Mullards were the choice, if given the $$$, but I just could not bear spending that much on a rectifier tube. I'd rather blow my $$$$$$$ on preamp and CDP tubes instead.

I have not had good luck with Sovteks. In my experience, they light up like Xmas trees too easily if you make a mistake in turning the amp on / off too quickly. I do, however, really like the JJ/Tesla 5AR4. Quiet (no buzzing), and pretty reliable so far. About $15 a pop new. Available at a variety of places, but I've always had some decent experiences with Tube Depot (on line).

Carl.

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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

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Very well described by Voodoo Doc in the earlier post. I think you can also use 5R4 as I think it has the same filament voltage. The only issue could be the first cap after the rectifier. Both 5Y3 and 5R4 would work better if the first cap is small; 10 mfd even smaller. However, if the 5Y3 is not arcing then I guess the cap is small enough and not a problem in your amp. The 5AR4 does not have the first cap issues, and also has a slow start. Personally, I like the 5Y3 as the voltage drop gives some motion to the music. Although the 5AR4 would provide more head room. With all that said, I don't think it makes sense to invest in NOS 5AR4s; $80? I would just use current production.

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Thanks to all for the input. Oh, welcome to our new members also.

I've been playing around with the different tubes. Looking for an edge in performance anyway I can get it, I bought a GrooveTube 5AR4 at BJ's Guitar Island on the southside of Indy (nailed me for $25+ tax on it) on tuesday and dropped it in. I let the AA-111 warm up about 5 minutes and hit the play on the cdp. I couldn't hear a difference even with the new tube. I had to leave for a while and left the amp, preamp, and tube cdp all playing on repeat. About 2 hours later when I returned I still couldn't hear any noticable difference in the amp. I Shut it down, let it cool off for about 20 minutes and put the 5Y3gt back in and fired it back up. If there is a performance difference in rectifier tubes with this little amp I couldn't hear it. One test doesn't make for solid experimentation but at this point and time I seriously doubt I'd shell out $70+ for a rectifier tube unless all I could buy were the GrooveTubes. I hate the big orange lettering on them.

Harry

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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

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Thanks for the tips. For me I won't be pushing the smaller Heathkit at all. I've got some monster power tubers and there's no need to hit the small one hard.

I do know where there are thousands of NOS tubes in Indy if you need any. For the most part they're very reasonable and using the price books from 20 years ago on them. I won't say where but I'm even buying nice power tubes at 1975 prices. Love it but I'm going broke jumping all over these. As you can imagine some of the different tubes are getting thin in stock and brand selection but it's surprising there's so many left.

I've used everyone on the list except for Triode Electronics. I've known Kevin for decades. Actually since he was "knee high". Tommy was the only person on earth I'd let touch any of my old Strats or my Martin D5.

Harry

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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

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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

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If the amp calls for 5AR4/GZ34, then I would try to stick with the indirectly heated rectifier it calls for. For the fact that it has a slow start feature(10-11 seconds?) from having a cathode.

The 5Y3 is a "instant on" (no warm up time) rectifier from being directly heated. You may have noticed when swapping the two in the amp. You throw the power switch, and the 5Y3 filaments instantly glow. where the 5AR4/GZ34 takes a brief time for the filaments to start glowing.

So when you throw the power, most the power/current hits the B+ supply input caps a bit harder and higher than the rectifier that uses a cathode with a warm up period. Really not much different than using a solid state rectifier if you think about it.

I suppose if the PS capacitors are rated high enough for the higher voltage/current on start-up, it isn't probably a big deal. But over a course of time with cycling the amp on and off using 5Y3, it may just tax the PS components a bit more than if using a 5AR4. I dunno...

Some rectifiers draw more filament/heater current than others. One needs to know the heater current for the rectifier, and the heater current output from the power supply heater winding for the rectifier tube. If the tube draws more heater/filament current than the PS winding puts out, then one will be taxing the winding. (a bit...or alot..depending.)

If the tube draws less heater current than the PS winding, then it is really no concern I guess.

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