BenC wrote:Hi marty_e!
Noticed you also used a GZ34/5AR4 rectifier. Is this tube a direct replacement of the 5Y3? Was there a noticeable sonic difference when the rectifier tube was replaced? TIA
Cheers,
BenC
Congratulations
marty_e!
Reading your post, like
BenC, I too am intrigued about the 5AR4 and 5Y3 statement. I can safely assume that this produced a big swing in performanced(sound) of the unit. Yes, one can interchange the two in terms of pin outs, but the 5AR4 is directly heated(DH) rectifier whereas the 5AR4 is a indirectly heated variety.
The 5Y3GT (directly heated) does not have the "soft start aka delayed start up time" feature that the 5AR4 has upon turn on. It all depends on the designer of the circuit where it is employed to provide a delay preventing cathode stripping of other subsequent tubes on the voltage path. What it does is it wil strip your other tubes(cathode-stripping)because there is no electron cloud formed yet in the tubes before high voltage were applied(prematurely)to the other circuit coponents after the rectification stage. The 5AR4 on the otherhand is a indirectly heated rectifier which has the safety turn on delay eliminating the occurence of the cathode stripping problem. That is why some circuit design using the 5Y3GT has a filament heater first before applying the high voltage(delay).
Here is a table of the typical "turn On" delay time (meaning full voltage appllied for maximum current)of some tubes:
5R4 5sec
5U4 6sec/6sec
5931 9s/7s/10s
GZ34 31s/33s/32s
PY88 40s
PY500A 45s/40s
Also, the 5AR4 has a lower voltage drop than a 5Y3, around 40 volts less than a 5Y3 at say 100mA current. So, replacing the 5AR4 with a 5Y3GT results in under voltage of other circuit stages that would shift all of the preamps operating parameters. Similarly, a 5Y3 designed PSU using a 5AR4 will produce an over voltage which will affect(shift) the preamps operating parameters to the other extremes. Guaranteed! Unless, the designer intended to use both tubes in the power supply and a voltage regulator with a wide range is incorporated in the design of the PSU.
For me, it is on plain view that changing the 5AR4 with the 5Y3GT or vice versa will change the characteristics(operating point of circuit elements, thus the sound) of the preamp and of course its "voicing". This can be proven very easily by measuring the rectified voltage (output) of the preamp PSU between two tubes. They are not the same. I would bet that changing the rectifiers will immediately results to a different sound of the preamp that is not subtle and much more discernable than comparing/rolling 6SN7's.
Now the big question, "Is a 5AR4 a
direct replacement of a 5Y3?" In plain view, it is not. One can take the place of the other but there are "precautions" that needs to be understood before doing so.
My above statements were from my experienced. I have been using an Octal preamp for two years now. It also uses a rectifier tube of either a 5AR4 or a 5Y3 family, has its own individual regulator stage (can use tubes like 5881, 6L6GC, El34, KT66, 6F6, etc.)per channel, and transformer coupled output. In my unit, changing the rectifier tube or the regulator tubes or both at the same time(although with this scheme, it was difficult to to pin point which one "contributed" more to the changes heard) project a bigger change of the sound as opposed to changing the 6SN7's.
mahalo