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It is currently 02 Jul 2020, 17:02

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PostPosted: 17 May 2020, 11:35 
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Joined: 04 Jun 2008, 20:59
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Location: Arizona, USA
Hi, I believe you have the answer. It is a socket or wiring connection. Resolder the tube socket connections. I would do the preamp tube first, but it really can be any of them. One can be intermittent and look fine. The number one problem with diy projects (except for not following the instructions) is bad solder joints. Most folks do not use enough heat. I use 775F. It is better to have high heat for a short time than lower heat for a longer time. Components are seldom harmed by short duration high heat, but can be by long duration low heat. Additionally, while I value the environment, I use only lead based solder. The amount that can find its way into the environment is zilch. The use of lead free solder is more difficult to use and get right. I have encountered many diy projects using it that are just chock full of "cold" solder joints and a nightmare to make work correctly.

Good listening
Bruce

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PostPosted: 17 May 2020, 23:46 
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Joined: 23 Feb 2017, 02:02
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I typically like 400C for high quality solder and 450-480C for very poor quality solder which should be disposed and not used.
I like 425C for moderate value solder.

Other than SMD capacitor and components that can eaisly be cooked, generall through hole components are quite immune to abbuse from soldering temp.

I like to use the weak acid solder paste which mainly is for cleaning the tip, then scrubb the tip on metal ball, then immerse the tip into cheap chinese flux which refreshes the tip to like new.
Also inexpensive to use and can last ten + thousdands of times before you run out.

Just a metal ball and cheap flux majority of the time the tip will be dirty and never work well especially high heat and poor solder quality.


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PostPosted: 26 May 2020, 14:19 
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Joined: 14 Feb 2010, 13:13
Posts: 707
Location: Lisbon, Portugal
Hi!
I'm I wonder what's the purpose of the 10uF Poly capacitor on the center tap of the OT?

Thanks!

Miguel


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PostPosted: 26 May 2020, 14:55 
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Hi, When I first designed these amps I noticed that the response did not quite measure up to what I thought it should. For want of a better term it seemed sluggish. Measured OK in steady state tones, but just didn't have that zing I expected when I listened to them on my electrostatics. The capacitor acts as a low impedance path right at the transformer and made the amps sound like I wanted. It is possible to omit it if you like the sound without it. Another similar mod is to use all polys or motor run capacitors in the power supply. Both will achieve the same end result. I figure that one 10uf poly is a lot cheaper than either of the other choices so that is what I did. BTW I did build one set of amps with all polys in the PS and it was fine, just as far as I could tell it sounded the same as using just one at the transformer. As always YMMV.

Good listening
Bruce

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PostPosted: 26 May 2020, 17:06 
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Location: Lisbon, Portugal
Thanks for the reply Bruce!
Tomorrow I'll try it!

Cheers!

Miguel


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PostPosted: 29 May 2020, 12:20 
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Joined: 01 Feb 2015, 13:41
Posts: 172
Location: Athens-Greece
Hi. I am thinking to build versions of EL84PP and KT88PP using the following Monolith transformers:
BA-14 (8K, 4-8 R) for EL84PP
BA-8/8K (8K, 4-8R) for KT88PP
Are they ok? They are expensive so they have to be well tuned.


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PostPosted: 29 May 2020, 13:49 
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Hi, I am unfamiliar with those transformers. One thing you need to be sure of is that they can handle the idle DC current and not saturate. For the EL84s the transformers need to handle at least 100ma and for the KT88s at least 200ma. I find typically that if a transformer is rated in watts it is for class AB use and will not be sufficient. Unless specifically indicated that the transformer can handle the DC I would go for ones that are at least 50% higher in wattage rating. Double is better, thus the 10 watt ones on the Poddwatts (they deliver 5 watts audio) and ones like the 70 watt ones on the KT120 (good for about 40+ watts) . The exception in the Edcor line is the CXPP25 ones. They are rated for the DC and the amps deliver about 25 watts of audio. It is however as I noted a happy exception.

Good listening
Bruce

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PostPosted: 18 Jun 2020, 09:55 
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Joined: 13 Jun 2020, 16:09
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My stereo version using KT77's. Antek power transformer, EM84 magic eye tubes, round LED style heatsink for the current source, high voltage delay relay. LED`s on the heatsink and tubes , bias test points on top of the chassis.


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PostPosted: 20 Jun 2020, 10:06 
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Hi, Nice looking build. I have a batch of the EM84s and considered them for use in the amps, but the "KISS" concept won out. What are you measuring with them? EM80s would be nice to have, but are now like gold for cost.

Good listening
Bruce

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