Grundig V5000 - German Masterclass

Hello Nikbad, I am sorry I missed your post completely. Thanks BufferBill for drawing my attention. The V5000 is a very good amplifier indeed and worth restoring. Do let me know what was actually wrong with it.

I got this amp, with a CF 5500 Cassette Deck and a Akai G630D r2r deck. The V5000 and CF5500 did not have their original packing but the Akai r2r deck did. Yes, I did see the import stickers on the box suggesting that it was imported into Iraq and thereafter brought to India.

The reel tapes which came with the r2r deck had hand written notes with comments on the content of the tapes. I handed these over to the new owner of the r2r deck, with the tapes. Regards.
 
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Hi Reuben and congratulations for V5000 restoration!
I also got at a fair price a V5000 but, upon opening the case to remove dust/clean pots etc., I found out that it was repaired and in a nasty manner, i.e. the driver transistors were of 3 different types (2 Gxxx original ones, 4xSC/SB, and 2 of other type), also the pre-driver ones (3 original ones and one BD135 if not mistaken). The amp was working but I decided to replace them so I bought 5xTIP35C, 5xTIP36C, 5xBD237, 5xBD238 and I plan to pair and replace the existing ones. My questions are:
1. You recomended in a previous post that testing should be done first at a lower voltage to minimise risk. Is it okay to plug the power cord in an 110V outlet (from a 220v - 110v transformer) to check the power amplifier stage at half of the specified voltage?
2. Can I test just the power amplifier stage only just by connecting the NF-Module board (the one with the capacitor bank, driver and pre-driver transistors) and the plug-in board (the vertical one with the bias current pots) and injecting signal at line voltage level (~300mV) to the input socket of the latter board (vertical one)?

Hope I made myself clear as english isn't my native language.
 
Hello Teo2005, welcome to our forum. Happy to be of help though its been quite a while since we completed the Grundig V5000 restoration and many other amplifiers have passed through my hands since. However I do recall some key moments of the restoration which included the search for G-series transistors. The transistor sets which you've bought are correct and will work well in your amp. Regarding your queries, here is my response:

1. You recomended in a previous post that testing should be done first at a lower voltage to minimise risk. Is it okay to plug the power cord in an 110V outlet (from a 220v - 110v transformer) to check the power amplifier stage at half of the specified voltage?

My response: The amplifier which you have is in working condition, even though there are substitute transistors used in the driver stages of the poweramp. Hence I suggest that it is safe to go through the replacement process and power up for testing using the in-built powersupply of the amplifier. The amplifier which we restored had a damaged PCB and someone had actually tried to modify the circuit to get it to sing. The amplifier was absolutely dead, nothing lighting up or firing. Hence what we did was we stripped it and took out the Power amp PCB, got it refurbished to factory specs and then implanted components using the actual factory specs again. We were not sure that the amp would work and hence we used a bench powersupply to power it up and see what happens. This approach is not required in your circumstances, in my opinion.

2. Can I test just the power amplifier stage only just by connecting the NF-Module board (the one with the capacitor bank, driver and pre-driver transistors) and the plug-in board (the vertical one with the bias current pots) and injecting signal at line voltage level (~300mV) to the input socket of the latter board (vertical one)?

My response: Yes you could do that and test with an injected signal. That's a simple approach. However since you have a working amplifier and are just doing a direct component replacement, things can go wrong only if you get the emitter, base and collector wirings for the transistors, messed up or if you don't have proper thermal contact between the transistors and the heat sink. If you are sure about getting these right, then you can go for a direct fire up and performance test using the regular sources that you have, via the amplifier preamplifier input.

This is a great amplifier and in any case, will sound really great. I found the presence control very useful. A true masterclass amp. All the very best.
 

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