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101D amp schematic.

90.149.215.224

Posted on September 21, 2014 at 01:00:56

iodemus
Audiophile

Posts: 170
Joined: October 21, 2010

I found this 101D/102D schematic from Valves World which make me able to build a modified version. Will this amp benefit from the feedback circuit or should I skip it? The resistor and cap have no values, what is appropiate?

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For what it is worth

Chip647

08:01:31 09/30/14

RE: 101D amp schematic.

Caucasian Blackplate

11:25:14 09/27/14

RE: 101D amp schematic.

iodemus

11:38:32 09/27/14

...

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For what it is worth

Chip647

08:01:31 09/30/14

RE: 101D amp schematic.

Caucasian Blackplate

11:25:14 09/27/14

RE: 101D amp schematic.

iodemus

11:38:32 09/27/14

RE: 101D amp schematic.

Caucasian Blackplate

14:27:47 09/28/14

RE: 101D amp schematic.

Paul Joppa

20:03:52 09/22/14

RE: 101D amp schematic.

Al Noakes

09:53:08 09/22/14

RE: 101D amp schematic. The aim.

iodemus

12:36:33 09/22/14

RE: 101D amp schematic. The aim.

Tre'

07:15:53 09/28/14

RE: 101D amp schematic. The aim.

Al Noakes

02:55:21 09/23/14

RE: 101D amp schematic. The aim.

iodemus

03:11:03 09/23/14

RE: 101D amp schematic. The aim.

Al Noakes

10:50:46 09/23/14

RE: 101D amp schematic. The aim.

Tre'

07:41:47 09/23/14

RE: 101D amp schematic. The aim. 10% distortion?

iodemus

08:28:18 09/23/14

RE: 101D amp schematic. The aim. 10% distortion?

Tre'

11:06:15 09/23/14

A little hard data from Western Electric

Tre'

18:30:23 09/24/14

Dave Davenport

18:27:58 09/21/14

Dave Davenport

09:08:47 09/23/14

Stuben

16:07:26 09/22/14

101D Schematic modifications

iodemus

22:03:37 09/21/14

RE: 101D Schematic modifications

drlowmu

09:05:02 09/22/14

RE: 101D Schematic modifications

iodemus

12:51:24 09/22/14

RE: 101D Schematic modifications

drlowmu

09:31:58 09/23/14

Triode_Kingdom

19:23:15 09/21/14

amnesiac

07:12:55 09/25/14

Dave Davenport

17:37:51 09/22/14

curious, posted on September 21, 2014 at 18:27:58
Dave Davenport Manufacturer Posts: 916 Location: North Carolina Joined: March 20, 2002	I am curious as the the purpose of the VR150 in series with the B+. Of course, it drops 150V, but I have a nagging feeling that it is there for some other purpose. Any ideas? Dave

RE: curious, posted on September 21, 2014 at 19:23:15
Triode_Kingdom Audiophile Posts: 10048 Location: Central Texas Joined: September 24, 2006	"I have a nagging feeling that it is there for some other purpose." Pilot light?

101D Schematic modifications, posted on September 21, 2014 at 22:03:37

iodemus
Audiophile

Posts: 170
Joined: October 21, 2010

The VR150 and the 47K resistor will be deleted in the modified schematic. A SEDHT circuit should be as simple as possible. It is no good construction practice to introduce resistance by hammering down the B+ voltage with a series resistor. The rectifier tube will be a RGN1064 followed by C-L-C-L-C. Film caps.
Each filament supply will employ Lundahl LL1694 double chokes in common mode rejection coupling and 2 x 15.000 microf. for zero AC.
There will be no feedback.
A switch for cathode current adjustment make it possible to use both 4101D and 4104D.
How does it look? Any critical and constructive suggestions are appreciated.

Johnny

RE: 101D Schematic modifications, posted on September 22, 2014 at 09:05:02
drlowmu Manufacturer Posts: 9730 Location: East of Kansas City Joined: January 10, 2005	You asked : (1) Simplify, get rid of the series coupling cap, and direct couple the the two audio stages. (2) Avoid a C input filter, puts spikes on B+. I like best of all .... L1/C1/L2/C2. Ls 20 Ohms or less in DCR, prefer under 10 Ohms. Jeff Medwin

RE: 101D amp schematic., posted on September 22, 2014 at 09:53:08
Al Noakes	'Will this amp benefit from the feedback circuit or should I skip it?' I'd skip that amp if I were you unless you have the valves in your stock . Even then I am doubtful about the design aims... Al

RE: 101D amp schematic. The aim., posted on September 22, 2014 at 12:36:33

iodemus
Audiophile

Posts: 170
Joined: October 21, 2010

Hello Al,

Feedback is skipped.
Of course I have several NOS in stock, rescued just before they went to the dump. Today they can fetch over $2000 per pair.
Replicas are made today. Why?
Because of the extreme accuracy and great fidelity.
101D tubes have found their new amplification today in extreme high end tube amplifiers. Extremely accurate low voltage amplification, greatest fidelity and linearity across all frequencies .. extremely hard to find today.
You need at least 100 dB horns for the 400-700 mW otput. Mine is 110 dB. 82dB speakers need >500 Watts for the same volume of nice music.

Johnny

RE: 101D Schematic modifications, posted on September 22, 2014 at 12:51:24
iodemus Audiophile Posts: 170 Joined: October 21, 2010	Hello Jeff, 1. It would have been fine to skip the coupling cap, but what are the consequences? I don't want to destroy the tubes and OPT's. How to make protection circuit? 2. Partially L input filter, only a very small C to get the B+ on the mark. 30 ohms each choke, the best I had. Johnny

RE: curious, posted on September 22, 2014 at 16:07:26
Stuben Audiophile Posts: 669 Location: Guber Ohio Joined: December 30, 2005	I've Always associated VRs with having inductive qualities.. A cheap choke with the paralleled resistance... Stuben

RE: curious, posted on September 22, 2014 at 17:37:51
Dave Davenport Manufacturer Posts: 916 Location: North Carolina Joined: March 20, 2002	Cool! Cool blue glow. Dave

RE: 101D amp schematic., posted on September 22, 2014 at 20:03:52

Paul Joppa
Industry Professional

Posts: 7296
Location: Seattle, WA
Joined: April 23, 2001

I agree about skipping the reg tube in that position - it appears to be there just to get rid of an excess power supply voltage, probably because that was what was in the designer's junk box ... it would be useful to find the original source of this circuit. Hammond makes a suitable transformer with lower-voltage secondary. Alternatively you could stack gas reg tubes to build a shunt regulator from the ground side, a simpler and more reliable approach IMHO.

Jeff is suggesting a quite different circuit topology, which among other things would require TWO independent floating filament supplies, floating at different voltages. It might sound quite good, but there is a lot of engineering between a topology described in a post, vs. a completed and tested design that is known to work with the component values chosen!

Not knowing the feedback resistor and cap values (at the top of the circuit) makes it difficult to predict anything about that portion of the circuit.

RE: 101D amp schematic. The aim., posted on September 23, 2014 at 02:55:21
Al Noakes	I think you will be hard-pushed to get anything like 400-700mW out of a 101D . I was under the impression these were only good for around 250mW hence my comment regarding the intended design goals . There is also microphony , which can be a major issue with using HE speakers with DHT amps Al

RE: 101D amp schematic. The aim., posted on September 23, 2014 at 03:11:03

iodemus
Audiophile

Posts: 170
Joined: October 21, 2010

Al,

I think you are a little pessimistic now.

Here is a link where you can read about the Yamamoto amplifier.

Johnny

Yamamoto 101D/104D amplifier.

RE: 101D amp schematic. The aim., posted on September 23, 2014 at 07:41:47
Tre' Industry Professional Posts: 17305 Location: So. Cal. Joined: February 9, 2002	Those power specs, .69 and .63 watts, are at 10% distortion not the usual 5%. Tre' Have Fun and Enjoy the Music "Still Working the Problem"

RE: 101D amp schematic. The aim. 10% distortion?, posted on September 23, 2014 at 08:28:18
iodemus Audiophile Posts: 170 Joined: October 21, 2010	10% distortion !! My first transistor amp fifty years ago had only 0.01%. So sad I scrapped it, I could have saved hundreds of dollars. Thank you for that information.

RE: curious, posted on September 23, 2014 at 09:08:47

Dave Davenport
Manufacturer

Posts: 916
Location: North Carolina
Joined: March 20, 2002

This nagging feeling has got me to thinking...

Perhaps the VR150 is a power-on delay for the B+.

- Until the triodes start conducting, there is no voltage drop across the VR150. The plates of the triodes are isolated by 47K from the power supply.

- When the triodes start conducting, the voltage across the VR150 starts rising. It rises slowly as the tubes heat up but the current through the tubes is limited by the 47K resistor.

- When the voltage across the VR150 reaches its firing voltage, the VR150 will start conducting; effectively bypassing the 47K resistor.

Clever.

Dave

RE: 101D Schematic modifications, posted on September 23, 2014 at 09:31:58
drlowmu Manufacturer Posts: 9730 Location: East of Kansas City Joined: January 10, 2005	A properly designed direct-coupled two-stage amp is hugely bulletproof. Start to study Loftin-White iterations on line. Usually B+ to the Finals is 450-500 VDC which most output tubes and transformers can take. I can send you information if you email me . Jeff Medwin

RE: 101D amp schematic. The aim., posted on September 23, 2014 at 10:50:46

Al Noakes

Yamamoto-san says :

'With this output power, since it seemed that it is too small, we decided to apply somewhat higher voltage to this vacuum tube'

Thrashing the poor things nutless , tennis balls like this need treating with respect . There are better valves to use as output stages , also running RL=Ra is a good way of generating excessive 2nd harmonic .
I have used 3A/141A which is STC's ST version of the 101D . It's best suited to line stage use

Al

RE: 101D amp schematic. The aim. 10% distortion?, posted on September 23, 2014 at 11:06:15
Tre' Industry Professional Posts: 17305 Location: So. Cal. Joined: February 9, 2002	My point was only about power. Not about sound. When we think of a 45 we think 2 watts at 5% distortion. A 2a3, 3.5 watts 5%. A 300b, 8 watts 5%. I think Al is right when he said "I think you will be hard-pushed to get anything like 400-700mW out of a 101D" at least not at 5% distortion. Take this info how ever you want to. Tre' Have Fun and Enjoy the Music "Still Working the Problem"

A little hard data from Western Electric, posted on September 24, 2014 at 18:30:23

Tre'
Industry Professional

Posts: 17305
Location: So. Cal.
Joined: February 9, 2002

1/4 watt at 5% 2nd HD, 1.4% 3rd.

If 1/4 watt is all you need, I'm sure it's a great tube.

Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"

http://www.westernelectric.com/spec_sheets/101D.pdf

RE: curious, posted on September 25, 2014 at 07:12:55
amnesiac Audiophile Posts: 717 Joined: August 21, 2002	Haha check the specs out of the a4714 and it will be telling as to the true purpose of the amp. One of sakumas early standards for preamp duty.

RE: 101D amp schematic., posted on September 27, 2014 at 11:25:14
Caucasian Blackplate Industry Professional Posts: 8313 Location: Seattle Joined: June 18, 2004	Why would you want to build a 2 stage preamp with feedback?

RE: 101D amp schematic., posted on September 27, 2014 at 11:38:32
iodemus Audiophile Posts: 170 Joined: October 21, 2010	Please read all the postings in the thread before you ask such a question: http://www.audioasylum.com/forums/set/messages/7/76103.html

RE: 101D amp schematic. The aim., posted on September 28, 2014 at 07:15:53
Tre' Industry Professional Posts: 17305 Location: So. Cal. Joined: February 9, 2002	"Mine is 110 dB" What speakers? Thanks. Tre' Have Fun and Enjoy the Music "Still Working the Problem"

RE: 101D amp schematic., posted on September 28, 2014 at 14:27:47
Caucasian Blackplate Industry Professional Posts: 8313 Location: Seattle Joined: June 18, 2004	You're going to end up with poor damping/distortion without the feedback loop.

For what it is worth, posted on September 30, 2014 at 08:01:31
Chip647 Audiophile Posts: 2652 Location: The South Joined: December 24, 2012	I have listened to 101d on efficient horns and they played nice at low levels, however turning them up slightly caused them to sound hard and distorted. That they will make a peak power of .6 watts at 10% distortion, the average listening level will have to be less than .1 watt not to clip on every peak. 0.1 watt ain't much. Make a headphone amp out of them.

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