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 NEW  Matt presents bias and operation data for the 6V6 tube in SE operation - 6V6 Single-Ended (SE) Ultra Linear (UL) Bias Optimization.

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PostPosted: 07 Feb 2018, 17:20 
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Joined: 14 Aug 2017, 11:03
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Location: Spain
The feedback is right, I know because first time I power the amp it was inverted (had positive feedback).

Perhaps the red plating is just because the Tung-Sol are not up to the original specification for EL34. Anyway I will try to post some pictures from the scope to the noise at the output and also on the cathode of the EL34.

Regards,

Iker.


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PostPosted: 07 Feb 2018, 19:58 
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Joined: 23 Feb 2017, 02:02
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Your valves could also been damaged from this first time it has gotten a red platting.


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PostPosted: 08 Feb 2018, 15:51 
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Joined: 29 Jun 2016, 15:59
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Team,

I know that, for heat considerations, it is better to mount the LM317HV and it’s heat sink outside of the chassis. However, I have seen some designs with it mounted inside. Is this OK? I could always make some openings on the plate for the air to flow.

I assume that it is OK to mount the FBR inside as long as there are some openings for the air to flow.

Thanks,


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PostPosted: 09 Feb 2018, 16:55 
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Joined: 04 Jun 2008, 20:59
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Location: Arizona, USA
Hi, The amount of heat developed by the LM317 depends on which tubes you are using. For example a pair of KT88s will cause it to dissipate about 7 watts. It doesn't sound like a lot, but inside a chassis it will build up and can cause failure of components. I always locate mine outside with the exception of the EL84 amps. In that case it can often be mounted (with insulator and heat sink compound) to the underside of the top of the chassis. They will dissipate around 1 watt. The bridge rectifier needs a bit of ventillation as well, but not as much as the LM317. It will be dissipating around 2 watts in the bigger amps. I like to place them off the circuit board and under a bunch of vent slots. The thing to remember is that heat is a killer of equipment. The less inside you have the longer the thing will function.

Good listening
Bruce

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PostPosted: 11 Feb 2018, 17:10 
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Joined: 16 Feb 2016, 19:45
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Location: Boston, USA
Just had a Shuguang "Gold Aero" KT88-98 fail open-circuit on it's heater after a few hundred hours. Expected? Don't think I did anything odd to it. Replaced it with another. Heater voltages (AC) measure 12.0VAC across two KT88 in series.

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PostPosted: 11 Feb 2018, 17:12 
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Usually DH tubes are failure prone in that way. Maybe it got bumped around too much in shipping?

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* Ratings are for transistors - tubes have guidelines*
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PostPosted: 14 Feb 2018, 18:54 
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Joined: 29 Jun 2016, 15:59
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Bruce & team,

Thanks for the replies.
How do you feel about use using double row terminal blocks to connect components on a board to other components in the amp? I.e., to make removing the board an easier task.


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PostPosted: 14 Feb 2018, 21:45 
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Hi, I have done that in the past. It works well. Now most of my prototypes are modular. I build the PS on one board, the active stuff on another and in some cases there are as many as 4 separate boards. I connect them with screw terminal blocks. It makes it easy to debug them if something doesn't work and easy to mod something. Just give thought to how you would service what ever you build. Since not everything goes as expected it is IMO one of the most important considerations in layouts and configuring the build. Space parts out and use a chassis at least 50% bigger than you initially thought you would need.

Good listening
Bruce

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PostPosted: 16 Feb 2018, 13:50 
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Location: Boston, USA
Any reason not to run KT120s in this design (at the KT88 90mA bias setting)?
A friend has offered to give me the ones from his (commercial) amp which
he just upgraded to KT150s.

I'm pretty sure my heater supply (XPWR117, AC heaters) can handle it.

I'm sorry if this was asked already in the forum, but there are 171 pages
to search now!

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PostPosted: 16 Feb 2018, 14:32 
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Joined: 29 Jun 2016, 15:59
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I have built the first PS board and now I am deciding whether to build the standard wooden chassy with an aluminum top plate or a solid wood one (wood alll around). I like the solid wood look. Especially when it is finished properly. But, are there any grounding/technical considerations?
If I go with a solid wood top, should I still put an aluminum plate under it?

Any advise will be appreciated. Thanks.


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