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A50 Mod Disaster
In Questions & Answers
Audio Valve Nut
DIY Champ
DIY Champ
Jul 07, 2022
Great New's , Good One Will
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A50 Mod Disaster
In Questions & Answers
Audio Valve Nut
DIY Champ
DIY Champ
May 26, 2022
Hi Mr Wilder, Looks like you have got yourself in to a bit of bother. Firstly did you do all the mods at the same time ? if so looks like you have several cans of worm's to sort out. Its time to clear your mind and start again. I had a similar problem a while back with a Pre Amp kit I built , I had an NPN transistor in were it should have been a PNP and my carrier is in electronics (Duh), it happens to the best of us. A circuit diagram shoes how it is all connected up and you don't have to understand it unless you are the designer but some understanding will help during fault finding.You need to be-able to look at the diagram and find things on the circuit board to test. If your not able to do that I suggest you find some body who can help you out with that. If somebody came to me with your situation I would probably tell them its quicker to strip it down and start again if multiple modifications have been added. Only do one mod at a time then test it before moving to the next one . This reminds me of my collage day's were we had to diagnose a fault with just a diagram and some voltages . I'll give you some pointer's to start with that may help. You say in your post that you took out all the tubes out and got no voltages anywhere , if you take out the rectifier tube then there will be no voltages supplied to the circuit. I am not being pretentious as how many of us have been testing for a power fault and one has not switched it on in the first place ( Put your hand up in the air if you have done this , there will be quite a few hand's in the air for that one) We will start with the basic's Safety first - you should be using an Isolation transformer to start with, if you are not then one hand in your pocket before you even start to test voltages, one voltage measurement at a time, switch off and let charge decay ( should be doing this any way don't care how experienced you are ). Make sure you are capable of using a multimeter buy selecting the correct Volt's, Amp's Ohm's for the measurement you are taking. PSU We will start with the Power Supply. All voltages supplied from the PSU must be checked even if things are working (your post-" The lights on the meters came on" probably ?? getting supplied from F1, F2 Mains Transformer ) as this can create Red Herring's and lead to confusion. I would replace the chard wire you talk of as you may have to change later on as it has been stressed. The way I would go about it is A,B,C,D as in diagram below , with Rectifier tube inserted. Disconnected were shown, Hand in pocket before Voltage Test's switch off allow to discharge for every measurement. As the PSU is effectively unloaded this should be done quickly but safely, watch that the voltage does not go above the reservoir capacitor max. voltage. If you check all the voltages from the PSU and they are correct I would then connect B2 then B+ . If all is correct I start would measure the voltages on the diagram starting with the pre amp section. If all the voltages are incorrect (don't now if diagram is before modification or after modifications) then I would put it back to its original working state before any thing else. This may be a lengthy process but that's what I recommend. Never Give In , Never Surrender Stay Safe Will
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Lucky Owner of A12 From Video Series
In Show and Tell
Audio Valve Nut
DIY Champ
DIY Champ
Apr 04, 2022
Fantastic
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The Sound Of Red-plating
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Audio Valve Nut
DIY Champ
DIY Champ
Mar 25, 2022
Tim Mellow - 25W OTL Tube Amplifier Build / Progress Just got some more kit that I may use for this Amp. All holes for Tube bases Done. Chassis now formed using my home made sheet metal bender. Seen this Double VU Meter with driver board on Ebay , ooh, thought I'll incorporate it in the design. Original design had 2 x 1Amp meter's for biasing only, no VU Meter's. I have read in some of the forums these meter's were replaced by resistors and not fitted after initial set up. I'm going to use a switch were I can switch between the resistors and meters so as to check the biasing now and again when needed. Trying to fit the 1 Amp meters any where on the chassis just did not look aesthetically right. Hole cutout for the Meter, took about an hour to complete , took extra care not to mark the chassis as this will be in full view when complete. Deciding were the I/P'S and O/P'S are going. Decided on this layout in the end. I ordered a pair of these with driver board some time ago to go with the Boyuurange A09 No lamp adjustment with this PCB Dam big holes to drill thorough the face plate. Made the mistake of measuring the resistance of all the meters and testing their deflection. 2 Pairs and I Double all varying resistances and deflections with the same current.The only consistency with parts from China is the Inconsistency. Best use these as "Indication Only" as they look like 20-30% variation between then. Having in the past calibrated Medical equipment these would be a nightmare to calibrate correctly and would be scraped. Tested using another Driver PCB with Lamp adjustment Low level adjustment High level adjustment Double vu meter Illuminated Added some tape to make them look better Take Care and have fun. Will.
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Trials and Tribulations
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Audio Valve Nut
DIY Champ
DIY Champ
Dec 15, 2021
Thanks and you take care
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Trials and Tribulations
In Show and Tell
Trials and Tribulations
In Show and Tell
Audio Valve Nut
DIY Champ
DIY Champ
Dec 15, 2021
Thanks and you take care
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New Breadboarded Amp(s)
In Show and Tell
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Audio Valve Nut

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