I want to learn about small frame grid triodes, how do they behave differently from a coiled grid triode in V1, splitter or driver positions? What was their reason to come into use? etc... I'm organizing tubes to clean the basement for Easter and see I have a crapload of 2HK5, 3HK5, 4HK5 and 6HK5 tubes. And probably other frame grid tubes too when I start to look them up. When I started this hobby I was buying TV-repair tube caddie's at swap meets whenever I saw one.
Google didn't bring up much about ?HK5 tubes for audio. Anyone try ?HK5 for audio?
https://frank.pocnet.net/sheets/201/6/6HK5.pdf
Google didn't bring up much about ?HK5 tubes for audio. Anyone try ?HK5 for audio?
https://frank.pocnet.net/sheets/201/6/6HK5.pdf
Most tubes can be used for audio. The biggest factor is linearity in the curves. Looks like the mu is high along with the GM. It might make a nice single stage driver for something larger. Just beware the ability to oscillate.
The datasheet leads me to think this is might be variable mu?
150 µmhos at Ec = -5V vs 1500µmhos at Ec = -2.6V ?
I can't find any curves, but since you have a bunch of em, you could just rig up a test jig and plot the curves on paper to see what they look like?
150 µmhos at Ec = -5V vs 1500µmhos at Ec = -2.6V ?
I can't find any curves, but since you have a bunch of em, you could just rig up a test jig and plot the curves on paper to see what they look like?
I could eTracer a few when I get some time, just have to make a config file for it so the eTracer knows what voltages to scan it with.
Is this tube the JEDEC equivalent to the European EC900? Some time ago, someone here has presented a RIAA preamplifier using it's series heated PC900 version.
Best regardS
Best regardS
Frame grid can be a little flatter, thus a little 'easier' to set close to cathode for high Gm.
They have a reputation for being screechy microphonic in audio. The frame grid wire is under tension, wound grids are not. I think a wound grid is low mechanical Q, but do not have data for that.
They have a reputation for being screechy microphonic in audio. The frame grid wire is under tension, wound grids are not. I think a wound grid is low mechanical Q, but do not have data for that.
I've heard quite the opposite, audio-wise. Due to the grid wires' tiny diameter (about one hundredth of a human hair's), their length, and their high tension, resonance frequency should be expected to be in the ultrasonic range. Anyway, I also do not have any robust data, especially not any measurements to back it.
Some decades ago I've build a tube preamplifier, comprising PCC88's exclusively. There are 12 pc., per each channel four in the RIAA section (with the triodes in each tube paralleled), two as line stage. I didn't notice any microphonics, not even in the RIAA eq. amp. And all my PCC88's weren't new, but pulled ones from old TV sets. I still have plenty of them.
Best regards!
Some decades ago I've build a tube preamplifier, comprising PCC88's exclusively. There are 12 pc., per each channel four in the RIAA section (with the triodes in each tube paralleled), two as line stage. I didn't notice any microphonics, not even in the RIAA eq. amp. And all my PCC88's weren't new, but pulled ones from old TV sets. I still have plenty of them.
Best regards!
Two (not 100 % identical) articles on microphony in tubes by Philips/Mullard.
The article from 1961 can be found on page 71 of this link: Philips Technical Review 1960/61
The article from 1962 is attached.
Frame grids are mentioned in the articles (a frame grid was made to vibrate at 37 kHz) but there's no real comparison between 'normal' grids and frame grids in the articles.
Like Kay I would expect that the resonance frequencies of frame grids are higher than those of 'normal' grids.
The article from 1961 can be found on page 71 of this link: Philips Technical Review 1960/61
The article from 1962 is attached.
Frame grids are mentioned in the articles (a frame grid was made to vibrate at 37 kHz) but there's no real comparison between 'normal' grids and frame grids in the articles.
Like Kay I would expect that the resonance frequencies of frame grids are higher than those of 'normal' grids.
Attachments
To quote mymyself:
"Towards the end of the valve era more and more valves (mainly television types) adopted ‘frame grids’. A frame grid has a pair of metal supports welded across the ends of the usual grid support rods to create a rigid, rectangular frame. This allows extraordinarily fine grid wire to be wound tightly across the frame, creating a flat or planar grid with better tolerances, which in turn allows the grid to be placed much closer to the cathode.6 Frame-grid valves therefore tend to have high μ and much higher gm than traditional types, and they can be more linear too, due to the more ideal parallel construction (the ECC88/6DJ8 is a popular example). However, despite having a more rigid frame, these valves suffer acutely from microphonics since even the tiniest movement of the grid amounts to a significant change in relative electrode spacings."
See: Mullard Ltd. (1960). Frame Grid Valves. Wireless and Electrical Trader, 8 October.
"Towards the end of the valve era more and more valves (mainly television types) adopted ‘frame grids’. A frame grid has a pair of metal supports welded across the ends of the usual grid support rods to create a rigid, rectangular frame. This allows extraordinarily fine grid wire to be wound tightly across the frame, creating a flat or planar grid with better tolerances, which in turn allows the grid to be placed much closer to the cathode.6 Frame-grid valves therefore tend to have high μ and much higher gm than traditional types, and they can be more linear too, due to the more ideal parallel construction (the ECC88/6DJ8 is a popular example). However, despite having a more rigid frame, these valves suffer acutely from microphonics since even the tiniest movement of the grid amounts to a significant change in relative electrode spacings."
See: Mullard Ltd. (1960). Frame Grid Valves. Wireless and Electrical Trader, 8 October.
Yes, everything resonates, unless it is sufficiently damped. But the question is: What's the resonance frequency? Is it within the range of human hearing?
Best regards!
Best regards!
There are multiple resonances and plenty of them are audible. Just listen to these tubes; they ring like bells.
Isn't this very tube specific ? E88CC don't seem to give audible sound when tapped at. Most cases of
microphony comes in my experience from tubes that has been subjected to harsh vibrations, such as
tubes mounted in guitar combos close to the speaker(s).
Not tube specific in my experience; all frame grids tend to ring more than regular types. If you put them in a guitar combo they would ring even more.
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