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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
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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
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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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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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PostPosted: 12 Oct 2020, 21:44 
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Hi, New addition to the amp family. A stereo integrated power amp with volume and balance controls and sufficient gain not to need a separate preamp. A more complete write up to follow later. It sounds just like the other Oddblocks (no surprise there). The extra stage has a gain of about 9 as shown with about a 50% loss in the balance control. Note also that a capacitive multiplier filter is used in place of the LR8 regulator. Only one channel of the filter section is shown so you need two of the CMs. The input stage of the amp is run full gain and can handle up to about 4 VRMS inputs without attenuation. It ought to be fine for most uses. If not then series resistors can be added to form a voltage divider there. The reason for not having the volume control there is to minimize hum and noise. As show it is really quiet. Under 1 millivolt of hum and noise at the output with full volume inputs shorted. I used a 6NO60 delay tube for warm up delay, feel free to do something else. I recommend a delay as the solid state rectifiers will hit the filters with over 525 VDC if the tubes are cold. Operating voltage is 475.

Good listening
Bruce
Attachment:
Stereo 20 OCT 2020.jpg
Attachment:
Oddwatt Integrated Stereo 10-12-2020.jpg
Attachment:
Oddwatt StereoPS 10-12-2020.jpg


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