Translated from Mr Ohashi's Blog
Difference Between Direct Thermal Rectifier Tube and Parathermal Rectifier Tube~
Dec. 13, 2024Today, I would like to write about the incoming inspection of rectifier pipes. Do you also sort rectifier pipes? Some of you may have wondered. Since the rectifier tube is what we now call a diode, basically if it has a function to convert alternating current into direct current, it will produce sound, and individual selection is not necessary.
However, in the case of some rectifier tubes, especially rectifier tubes that intentionally increase the internal resistance and have the same in-pipe drop voltage as the vintage 274B, such as the PSVANE WE274B that was inspected today, there will be a difference of up to several percent in the regulation (rectification efficiency) between individuals, so it is an effective method when you want to align the DC environment of two units by updating the rectifier tube of a mono amplifier. It is also useful if you want to check how much it has deteriorated in the case of old rectifier pipes.
It was tested by PSVANE WE274B. When checking the rectifier tube, the difference does not appear unless it is an amplifier with a large current consumption, so today we will compare the rectification efficiency of each rectifier tube by measuring the actual current with the SV-91B / Western Electric 300B specification.
In this case, what is needed is a constant voltage power supply. Since commercial 100 V is constantly fluctuating, the accuracy of the measurement cannot be guaranteed unless the primary voltage is accurately regulated. Also, like other vacuum tubes, the rectifier tube requires a certain amount of time to stabilize from the power supply, so it is meaningless unless the measurement timing is the same, so prepare a kitchen timer.In the PSVANE WE274B that arrived this time, all the currents on the SV-91B were distributed between 1.95A ~ 1.98A, and there was not a single individual that showed any abnormalities. By the way, the situation is almost the same with the Western Electric 274B, so it can be said that the manufacturing quality is properly controlled when it comes to the lot now.
By the way, if you replace it with Mullard GZ37 under the same conditions, it will flow about 2.1A. This can be explained by the fact that 274B is direct and GZ37 is paraheat. In other words, it indicates that the parathermal type has better regulation, and the same behavior is shown in Western Electric 422A.
Simply in terms of rectification efficiency, it can be said that the paraheat type is superior, but there are many people who feel sympathy for the smooth sound quality peculiar to direct heat rectifier tubes, and it should not be talked about simply as superior or inferior as it is the same as the taste preference of food.
In the case of amplifiers that can use both direct and parathermal types, such as SV-EQ1616D and SV-Pre1616D, the sound quality varies considerably depending on the rectifier tube, so if you are inexperienced, it is a good idea to try it. The reason why 5AR4 / GZ34 is said to be powerful and 274B is said to be delicate is that the rectification efficiency changes depending on the difference in structure, and as a result, the plate voltage of each amplifier tube changes.
Thank you Victor for the above post!
I'm new to DIYAudio forum but have been following various threads over the last 20 years related to various interests. It's always a treat to discover new and informed discussions, many have been very helpful!
Question for the forum regarding to the Level control on the Preamp:
At the beginning of the thread Victor posted: "Input Volume: Yes"
Is his post in reference to the Level control acting passively into the gain stage.
Or does the Level control increase output voltage - dB? (i.e., What does the Level control actually do?)
I don't see another pot that would suggest the Preamp is able to adjust both the source input and output.
Given my question I'm sure it's apparent that I've never built a component.
Thank you for your patience with a relative newbie to amplification.
Ward
I'm new to DIYAudio forum but have been following various threads over the last 20 years related to various interests. It's always a treat to discover new and informed discussions, many have been very helpful!
Question for the forum regarding to the Level control on the Preamp:
At the beginning of the thread Victor posted: "Input Volume: Yes"
Is his post in reference to the Level control acting passively into the gain stage.
Or does the Level control increase output voltage - dB? (i.e., What does the Level control actually do?)
I don't see another pot that would suggest the Preamp is able to adjust both the source input and output.
Given my question I'm sure it's apparent that I've never built a component.
Thank you for your patience with a relative newbie to amplification.
Ward
Thank your for your timely reply Victor!
However, my knowledge of electrical circuits is very limited! At best I would be guessing as to what this means.
Thank you in advance for any further info that could be provided.
However, my knowledge of electrical circuits is very limited! At best I would be guessing as to what this means.
Thank you in advance for any further info that could be provided.
From looking at your diagram and the pics of the inside of the preamp it looks like the Level control is active rather than passive. That is, the Level control adjusts the amount of amplification (volts/dB) that is sent to the RCA outputs rather acting as a passive volume before amplification adjusting the input of the source.
Hence, it appears that the Level control directly affects/regulates the amount of volts/dBs that are sent to RCA output.
Some preamps I've seen have adjustments for both passive input (source) and active output (adjusting how much gain is added to the output into a power amp). One of the posts above suggested to a member that they swap the Level control for a passive stepped attenuator (at least that was my understanding), which created further questions regarding what the Level control was actually adjusting.
Am I understanding correctly?
Hence, it appears that the Level control directly affects/regulates the amount of volts/dBs that are sent to RCA output.
Some preamps I've seen have adjustments for both passive input (source) and active output (adjusting how much gain is added to the output into a power amp). One of the posts above suggested to a member that they swap the Level control for a passive stepped attenuator (at least that was my understanding), which created further questions regarding what the Level control was actually adjusting.
Am I understanding correctly?
Please forgive my limited knowledge and misunderstanding of electronics!! This is apparent in my posts above!
I am only interested in your products and how they function, given I am interested in purchasing a number of items: S1616D, Pre1616D, & EQ1616D.
It looks like the Level control adjusts the gain of the amp.
I hope that I have that correct.
Are prices posted in CAN currency?
Thank you for your patients with this very new newbie!
Ward
I am only interested in your products and how they function, given I am interested in purchasing a number of items: S1616D, Pre1616D, & EQ1616D.
It looks like the Level control adjusts the gain of the amp.
I hope that I have that correct.
Are prices posted in CAN currency?
Thank you for your patients with this very new newbie!
Ward
WardAR, Post 44 shows the input jacks, the input select switch, the balance control, the volume control, then through a resistor to the grid of the input tube (not shown). (Or maybe it's the volume and then the balance, I forget which it's been years since I built one.) This is the typical layout of most line stages i.e. the gain of the circuit is fixed and what the volume control does is adjust how much signal is applied to the input of the active circuitry. Hope this helps.
S.
S.
The wiring runs from input selector to balance pot to volume pot, then to the circuit. The issue you might have replacing the pot is that the chassis hole for the supplied pot is too small for an Alps or a stepped attenuator. You would have to drill it out. For my build, I decided not to bother.
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