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Old 16th September 2021, 01:53 AM   #541
bondini is offline bondini  Australia
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01A question
Default Thnx Magz

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Old 16th September 2021, 02:42 PM   #542
merlin el mago is offline merlin el mago  Catalonia
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Quote:
Originally Posted by Magz View Post
Actually, it appears I can attach a .zip file so here is a zip of the excel calculator for lossy parafeed (DrP).

If you're using a CCS, the plate choke value can be set to a very large value to simulate.
Many thanks Magz.
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Old 16th September 2021, 10:51 PM   #543
nashbap is offline nashbap  United States
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Quote:
Originally Posted by bondini View Post
Hi magz, nashbap

If you're looking for a compact reference on designing for that resonance, Frank's electron tube data has a copy of Terman's 1943 Radio Engineer's Handbook here: electron Tube Data sheets - No brand related documents

Beginning on page 371 there is a discussion of "Miscellaneous Coupling Systems for Audio-frequency Voltage Amplifiers". The discussion of "Transformer Coupling with Shunt (Parallel) Feed" begins at the bottom of that page, with relevant graphs at Figure 14 (b) on page 374 illustrating the effect of altering the value of the coupling or "parafeed" capacitor.

Enjoy

I downloaded Terman's handbook and went thru the relevant pages. I experimented with the cap value and the effect is as represented in fig 14b.

Thank you for posting this info in the thread. It will come in useful.

nash
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Old Yesterday, 12:13 AM   #544
nashbap is offline nashbap  United States
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Originally Posted by Magz View Post
I have a neat little Excel spreadsheet posted online about a decade ago by a guy named VoltSecond that allows one to calculate the proper cap and resistor values and shows the resulting frequency response and PSRR for two different designs at a time.
I don't see a way to attach a .xls file on this post or I would do that. Instead I attach a screenshot of the graphs showing the peaking with just the 1uF cap (design 1 in blue) and with the 1uF and 3.3uf-8080R in parallel (design 2 in green). It's clear how design 2 minimizes the extreme peaking while still leaving a bit of bass boost in the lower frequencies. I have verified this behavior with measurements.

Based on your experience, I decided to experiment a bit.

I was getting a peak around 25hz of about 7db higher than the flat line somewhat like your blue line but not as severe a peak as yours. I have built according to Ale Moglia's LowGain model that has a 0.22uf coupling cap and a 510k resistor after it to G.

First, I paralleled 0.5uf with the 0.22uf and found that the peak remained at 25hz but it had dropped to about 3.5db and the curve portion less than 25hz was now sloping very gently upwards.
Next, I combined a 10k resistor to the 0.5uf and paralleled the combination to the 0.22uf cap. Wow, the peak dropped to only 2.5db and the the curve portion less than 25hz was now very gently sloping downwards. Also the peak had nicely rounded out. Next, I substituted a 20k for the 10k . Here I found that although the peak had remained about the same, the portion of the curve below 25hz was now sloping down, maybe a bit more than your green curve. What you have suggested most definitely works. Thank you!

I downloaded the zip file you attached, but am a bit confused as to how to use it. I entered 0.22 under C Parafeed Design2 keeping all else unchanged and Dr P optional Parts shows

0.44 0.44 uF est. 597149 8285 Ohms
Not sure how to interpret this.

nash

Last edited by nashbap; Yesterday at 12:17 AM.
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Old Yesterday, 01:23 AM   #545
Magz is offline Magz  United States
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To use the calculator you need to fill in all the values in the Design 1 and Design 2 columns D and F. Columns D and F are all you need to enter, the rest are calculated by the spreadsheet. C_Parafeed is your small cap. C_DrP is your larger cap. R_DrP is the resistor in series with the large cap. The diagram on the right shows what the component names correspond to. Usually I put the plain parafeed as Design 1 and the lossy parafeed as Design 2 so I can see the differences.
The results appear in the lower section, Output Peaking, -3dB Frequency, etc. and in the graphs.

Just play with different C_Parafeed, C_DrP and R_DrP values to get the peaking reduction and bass extension you want.
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Last edited by Magz; Yesterday at 01:39 AM.
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Old Yesterday, 02:35 AM   #546
Magz is offline Magz  United States
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Also, if you are using a gyrator load on the 01A use the output impedance of the gyrator instead of the 01A plate resistance in the calculator. I used a value of 1500 ohms as that was my estimate of the CCS mu output impedance on top of the 01A.
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Old Yesterday, 07:17 PM   #547
nashbap is offline nashbap  United States
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Got it. Thanks.
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