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PostPosted: 10 Oct 2017, 05:34 
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Joined: 24 Oct 2010, 07:05
Posts: 295
johndravo wrote:
Does it have to do with the separate grounding of the two power supplies to the chassis
I'm in doubt that it is the case.
johndravo wrote:
Can it be a big inrush current at the lr8s that causes them to shut down ?? (I am using 4uF of poly capacitance at their output)
Possible, but in several other use cases I saw 100uF after them and all works well.
I think the LR8s (to power B+) are dead or there is a mistake in wiring.
By the way:
johndravo wrote:
I made two power power supplies one for every channel using the lr8-k4g in the driver supply and I used one lr8 for the heater bias. I used a single large toroidal transformer with 2x 0-360V 200mA and one 12V 6A heater winding. The drivers are dc heated while the outputs are ac heated.

Had you doubled the heater bias circuits for each channel?
How did you manage to power the heaters both DC and AC from one winding?
Where did you connect the heater lifting point (to AC or to DC part)?


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PostPosted: 10 Oct 2017, 08:14 
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Joined: 05 Dec 2015, 14:00
Posts: 4
Thanks for the input poty!. Actually I found out it was a case of cold joints and after resoldering now everything runs smoothly. :D
The dc for the driver heaters is derived by a rectifier+capacitor in parallel with the output ac heaters like in the valve wizard heater article.

http://www.valvewizard.co.uk/heater.html

Nothing is grounded and the 80V lift is connected to the negative of the dc heater circuit. This way the lift voltage is measured also in the ac side. Have I done something wrong ? I am not an expert just an amateur learning slowly...
Also a final question: To eliminate the faint transformer buzz from the switching of the relay can anyone recommend some type of soft start device perhaps an NTC thermistor instead of the type X2+ 220R between the relay contacts ?


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PostPosted: 16 Oct 2017, 09:30 
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Joined: 01 Apr 2017, 19:56
Posts: 49
Hello Bruce and Oddwatt forum friends.
Quick question. Despite changing the SRPP tube to a 12ax7 type, is there any other way to increase the amplifier gain? I would like to connect a smartphone or mp3 player directly to it. Currently I have a JJ 5751 and KT88 outputs, built with the latest schematics (1200 ohm cathode resistors on the SRPP and 295V source). Thanks.


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PostPosted: 17 Oct 2017, 04:41 
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Joined: 24 Oct 2010, 07:05
Posts: 295
I think with modern devices you don't need the mod. There were several proves about that, including the Bruce himself: viewtopic.php?f=9&t=43&p=27102&hilit=pass%2A+pre%2A+Oddwatt#p27102


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PostPosted: 17 Oct 2017, 08:21 
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Joined: 01 Apr 2017, 19:56
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My portable devices can only output about 0.5 V Peak. Not even half what is needed to drive the Oddblocks to full power.


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PostPosted: 17 Oct 2017, 08:45 
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Joined: 24 Oct 2010, 07:05
Posts: 295
Do you need full power from Oddblock?
I'd not recommend to use 12AX7 in the driver position. On the other hand: there are so many inexpensive devices like buffers, preamps, headamps... It's even possible to put a small JFET amplifier right insight of the Oddwatt near the input RCA.


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PostPosted: 17 Oct 2017, 11:58 
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Joined: 29 Jun 2016, 15:59
Posts: 66
Sorry if you already saw this. By mistake I posted it in the general forum. Anyway, here it goes...
Thanks to Gregg for his reply.

Hi.

I decided to build the Oddblock monoblocks from scratch and would appreciate some help in selecting parts (I am not an experienced DIY). I have figured-out most of the parts, except for:

1) For the 0.1uf bypass capacitors across the B+ electrolytics in the power supply, I plan to use Polypropylene. Mouser does not show "audio grade" types. But has "AC and Pulse Film Capacitor", "General Film Capacitor", "Safety Film Capacitor", etc. I guess that I can use any of these. But, some of these state "not across the line" applications. Does this apply in this case? Or do I avoid them?

2) Can the same type of caps be used for the 0.1uf ones across the heaters?

3) The PS shows a DPST power switch. I assume that there is a reason for this (I would have used a SPST). I guess both poles would be connected to the Hot wire?

4) For the line filter unit, any of these 2 would do? The second one is twice as expensive and has more filtering:
Part # 3EHG1-2:
http://www.mouser.com/ProductDetail/TE- ... 9mnFXsw%3d

part # 3EGG8C-2:
http://www.mouser.com/ProductDetail/TE- ... 2fG0Fbk%3d

Any help is appreciated and sorry if these questions are too simplistic. Thanks.

Danny


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PostPosted: 18 Oct 2017, 12:17 
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Joined: 01 Apr 2017, 19:56
Posts: 49
If I were to implement a Forewatt in the same enclosure as my (stereo) Oddblock using the same LR8 regulated power supply (300 V output), would it be better to use a series resistor to drop the voltage to 215 V (18k ohms @ 4,54 mA). Or to substitute the cathode resistors on the Forewatt (from 470R to 1200R)? Thanks.


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PostPosted: 19 Oct 2017, 13:38 
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Joined: 24 Oct 2010, 07:05
Posts: 295
Danny wrote:
1) For the 0.1uf bypass capacitors across the B+ electrolytics in the power supply, I plan to use Polypropylene. Mouser does not show "audio grade" types. But has "AC and Pulse Film Capacitor", "General Film Capacitor", "Safety Film Capacitor", etc. I guess that I can use any of these. But, some of these state "not across the line" applications. Does this apply in this case? Or do I avoid them?
I'm risking to start a fierce discussion, but... You may look through other sources like partsconnexion to get "quality capacitors". In my opinion you may use polypropylene capacitors with good parameters (not "application") like ESR (tan of losses) too.
Danny wrote:
2) Can the same type of caps be used for the 0.1uf ones across the heaters?
Yes, but too expensive. There are a lot of much cheaper low voltage polypropylens (WIMA MKP2, MKP4..., Panasonic SMF...).
Danny wrote:
3) The PS shows a DPST power switch. I assume that there is a reason for this (I would have used a SPST). I guess both poles would be connected to the Hot wire?
This part can be made in several ways. It is up to your taste.


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PostPosted: 20 Oct 2017, 04:19 
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Joined: 24 Oct 2010, 07:05
Posts: 295
Danny wrote:
Part # 3EHG1-2:... or part # 3EGG8C-2:
It depends... If your mains uses safety ground (the third wire in the outlet) then it's better to use the second. Otherwise the added complexity does not make any sense.
victorzwk wrote:
If I were to implement a Forewatt in the same enclosure as my (stereo) Oddblock using the same LR8 regulated power supply (300 V output), would it be better to use a series resistor to drop the voltage to 215 V (18k ohms @ 4,54 mA). Or to substitute the cathode resistors on the Forewatt (from 470R to 1200R)? Thanks.
The total current for LR8 seems to be almost the max allowable and I don't know if it can cope with dissipation.
I'd use either dedicated LR8 for each stage or some combination of RC and LR8-C.


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