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Old 24th May 2011, 02:08 AM   #1
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Default Valve Amplifiers 3rd edition Errata

Hello,

I am working my way through Morgan Jones' Valve Amplifiers 3rd edition with the aim to build the line stage on page 576 (fig 7.41) and the power supply on page 374 (fig 5.48). So far it is a fun read and reread but I have hit a couple of stumbling blocks and would appreciate any feedback.

1.) On page 374 in figure 5.48, the schematic appears to correctly list the HT transformer at 625-0-625V but the description on page 372 under the heading "The HT supply" suggests 525-0525V. The written description on page 372 seems like a misprint since the voltage would be too low after the choke to support the 493V listed at the choke/snubber/regulator junction.

The link below to the google preview of the book shows figure 5.48
Valve amplifiers - Google Books

2.) The connection running from the heater regulators (317T inputs) to the collector of the MJE340 seems like it should be connected. It also appears this wire should loop over the wire coming from the lead of the adjacent transformer.

Lastly, does anyone know a list of errata for this edition?
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Old 25th June 2011, 10:55 PM   #2
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Still working thorough Valve Amplifiers 3rd edition and find the connection (lower right hand corner of the following link) running from the heater regulators (middle 317T inputs) to the collector of the bottom MJE340 seems like it should be connected. It also appears this wire should loop over the wire coming from the lead of the adjacent transformer.

Valve amplifiers - Google Books

Has anyone here built this supply or similar?

Any recommendations are appreciated.
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Old 25th June 2011, 11:23 PM   #3
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You are correct- that figure is somewhat bunged up. Your inference of the proper connections looks correct to me. There's a few errors here and there that have been found and forwarded to the author, who promises to correct them in the 4th edition (out later this year).
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Old 28th June 2011, 02:46 AM   #4
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Hello Sy,

Thank you for the help and information. Given the 4th edition is due out near the end of this year, might you have any other book recommendations? Also, if you could shed any light on the questions below I would appreciate it. For clarity, I am only building the (6s45pi with a EF184 cathode load) line stage on page 576 (fig 7.41).

Based on the description in chapter 5, the LT portion of the power supply circuit is intended for series heaters and use of the THINGY is ruled out on page 576 of chapter 7. Would it be wise to use the corresponding portions of the LT supply section for the heaters of the left and right channels in series? For example, can the elevated LT supply be used for the left and right 6s45pi heaters in a series configuration? Likewise can the earthed LT supply be used for the left and right EF184 heaters in a series configuration?
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Old 28th June 2011, 02:58 AM   #5
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Yes, no reason at all not to put the two channels' heaters in series. You could use a THINGY to elevate the heaters of the top tubes. As a practical matter, I never found the need to use a THINGY- a simple resistor string bypassed to ground always seemed adequate. A THINGY won't hurt, and if you have a tube with excessive heater to cathode leakage, it could be advantageous.
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Old 28th June 2011, 10:36 AM   #6
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While we're at it, look at Fig. 7.27 on page 543 in the 3rd edition. 2nd opamp from the left. That 33k resistor is miswired. The same mistake also appeared in the 2nd edition, as far as I remember.
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Old 19th July 2011, 06:27 AM   #7
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Hello Sy,

Thank you for the help.

Errata List
Based on the description prior to fig. 5.46 (page 366), the LT supplies do not appear to be drawn correctly either. In particular, the connection of the THINGY to the elevated LT supply.

Veering from the book examples
Since the preamp of fig 7. 41 (page 576) requires elevated heaters, and the 6C45PI heater requires Ih=400mA and the EF184 requires Ih=300mA, I am considering parallel heaters. The supply layout is based on fig 5.46 (page 366) but with chokes and turn-on circuitry similar to figure 5.48 (page 374) .

Is there is a good workaround to use only one choke for all of the heaters, or is a separate choke for each of the LT supply pairs required? In other words, the elevated LT supply for the 6C45PI heaters (L and R channels) requires a choke and the LT supply for the EF184 heaters requires another choke?
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Old 19th July 2011, 09:30 AM   #8
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Yes, if you use chokes, you'll need separate ones. Personally, I don't see the need, especially if the heater transformers are separate from the high voltage transformers. In my line preamp (also a CCS-loaded CF), the heater supplies are very simple- but regulated- and the noise levels are fabulously low. You can also use the trick from His Master's Noise and use a pair of regulators to drop the common mode noise as well.

If you use a solid state CCS, you eliminate the heater supply for the pentode. I suspect that Mr. Jones would approve.
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Old 23rd July 2011, 06:11 AM   #9
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Quote:
Originally Posted by Rodeodave View Post
While we're at it, look at Fig. 7.27 on page 543 in the 3rd edition. 2nd opamp from the left. That 33k resistor is miswired. The same mistake also appeared in the 2nd edition, as far as I remember.
Hello,
Could be my error, I built the Master (317) slave (Op-Amp) voltage regulators from the book and the magic smoke came out.
I retried the effort using the circuits in Joe Curcio’s Daniel amplifier with good results. For Joe Curcio see curcioaudio.com you also can see his work in white papers at National Semiconductor National.com. National originated use of the 317 in series high voltage regulators way back when.
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Old 26th July 2011, 03:35 AM   #10
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Hello Sy,

Thank you for your help. The "His Master's Noise Approach" is appealing -- perhaps phase II of the project.

The following is not an error but it is unclear. Based on the description in the chapter, the examples shown in schematics 5.46 (page 366) and 5.48 (page 374), what are the inductances of the two common mode chokes?

On the inlet (figures 5.46 & 5.48,) the choke is listed as 15T (turns) with 1.6mm wire but the core size and permeability are not listed.

In figure 5.48, between the reservoir capacitor and regulators, the description of the choke is 25T (turns) with 1.0 mm wire on a 30 mm core but the core height and permeability are not specified.

Also, are there recommended relays (based on figures 5.46, 5.48, and 7.41) to use for the audio signal muting and the heaters?
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