Hello, I have a Sweet little ‘lunch box’ amp that I am renovating at the moment. A Dynacord sv 17. I want to use this as a guitar amp and I thought I would go through it and change the electrolytic capacitors and any other parts that don’t measure up to par. Everything looks original and judging by the dust inside, untouched. Now I have come to my first hurdle. There are two large can caps between the transformers. Both are marked Dynacord and have values of 32+32/550v and 32+32/385v. The problem is that according to the schematic it should be 32+32 and 16+16. At first I thought the second one might be wired up in series, but it doesn’t look like it. Before I order some cans from Jan Wuesten I just wanted to ask if I should go by the schematic or replace the old cans with the same values as found in the machine? Maybe someone here has some experience with these amps.
Thank you for your help!
Lucas
Thank you for your help!
Lucas
Hello Again, I now have my second hurdle, the resistor between pin 3 of the ez81 that runs to the + pole of the second section of the first 32uf cap is marked in the schematic as 5,1k. In my machine it is a 56 ohm 2 watt resistor! That is a huge discrepancy! Unfortunately there are no voltages marked in the schematic, (which I downloaden from the internet). I am going look for some gut shots on the Internet to hopefully get a comparison but there is not too much out there about the sv17.
Cheers
Lucas
Cheers
Lucas
If it worked properly for 50 years I would respect values actually there.
To boot I guess those caps were fit at factory, *they* should know.
As of:
You will do more damage than good.
EDIT:
Are we supposed to use a crystal ball? .....
To boot I guess those caps were fit at factory, *they* should know.
As of:
what do you plan to do? Remove every single part to measure it and compare to printed value?
You will do more damage than good.
EDIT:
I must need new glasses because I do not see the schematic.......
Are we supposed to use a crystal ball? .....
Last edited:
Thank you Fahey for your answer.
I don’t know when it last worked properly, but I did find a photo of the innards on radiomuseum, and I am now almost convinced that someone changed the 5,1k resistor and maybe reading the value incorrectly, replaced it with 56 ohms.
What do I plan to do? Yes I will measure every component in there and if they are off I will replace them with the proper value according to the schematic. However this can be problematic if the schematic has a mistake or there are different versions, which is why I then compare the components to other existing models and ask experts in forums. Afterwards I might do some modifications to get the sound that I want. I like to keep things as original as possible, so usually I just replace the electrolytic or dried up paper capacitors and some resistors and tubes if necessary, clean the potentiometers and make sure the voltages are healthy. In this case, the amp was designed for use with early phonographs and has a push/pull volume pot that routes to a another pot with 4 different equalization settings, (Entzerrung). This could be easily changed or modded for guitar use. As far as doing more damage than good, I am very careful and patient and if a part is working then it stays in, except for the electrolytics which are now over 60 years old and there is no reason to keep them.
Cheers,
Lucas
I don’t know when it last worked properly, but I did find a photo of the innards on radiomuseum, and I am now almost convinced that someone changed the 5,1k resistor and maybe reading the value incorrectly, replaced it with 56 ohms.
What do I plan to do? Yes I will measure every component in there and if they are off I will replace them with the proper value according to the schematic. However this can be problematic if the schematic has a mistake or there are different versions, which is why I then compare the components to other existing models and ask experts in forums. Afterwards I might do some modifications to get the sound that I want. I like to keep things as original as possible, so usually I just replace the electrolytic or dried up paper capacitors and some resistors and tubes if necessary, clean the potentiometers and make sure the voltages are healthy. In this case, the amp was designed for use with early phonographs and has a push/pull volume pot that routes to a another pot with 4 different equalization settings, (Entzerrung). This could be easily changed or modded for guitar use. As far as doing more damage than good, I am very careful and patient and if a part is working then it stays in, except for the electrolytics which are now over 60 years old and there is no reason to keep them.
Cheers,
Lucas
Maybe this schematic is better.
As Fahey said:
"If it worked properly for 50 years I would respect values actually there."
Dynacord is a manufacturer that knows what it's doing.
An example of good workmanship.
I worked on them over the last half century. If only all mfg's were the same...
Caps from AJF are excelent. Probably he has the same mechanical versions.
Nice to convert to a guitar amp.
As Fahey said:
"If it worked properly for 50 years I would respect values actually there."
Dynacord is a manufacturer that knows what it's doing.
An example of good workmanship.
I worked on them over the last half century. If only all mfg's were the same...
Caps from AJF are excelent. Probably he has the same mechanical versions.
Nice to convert to a guitar amp.
Thanks for that Tarzan, I was having trouble uploading my files.
I was looking around for similar designs and the dynacord da16v is quite similar except it has tremolo. There are also 2 x 32+32uf can caps and a 5,1k resistor between the first and second section of the first can.
I was looking around for similar designs and the dynacord da16v is quite similar except it has tremolo. There are also 2 x 32+32uf can caps and a 5,1k resistor between the first and second section of the first can.
Note those very unequal plate and cathode resistors in the Concertina PI!
OTOH you have the basics there that would allow you to clone a Marshall preamp and PI section. That's what I would do if I had the same intention as you. Another option would be cloning the Carmen Ghia amp, with only two ECC83's and only the knobs that really are necessary for a good tone.
Best regards!
OTOH you have the basics there that would allow you to clone a Marshall preamp and PI section. That's what I would do if I had the same intention as you. Another option would be cloning the Carmen Ghia amp, with only two ECC83's and only the knobs that really are necessary for a good tone.
Best regards!
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Thank you for your answer Kay. Note taken! First I want to find out how this amp sounds from the original design, afterwards the fun can begin. What do you make of the discrepancy between the 56ohm (found in amp) and the 5,1kohm (as in schematic) resistor between the 2 sections of the first 32uf capacitor? I am thinking that somebody was trying to compensate for a dying ez81. I wish there were some voltage references written somewhere but I can compare it to some other designs.
Best regards
Lucas
Best regards
Lucas
The schematics in #5 show 5.1 kohms for this resistor, so go for it. Just 56 ohms in this role is next to nothing.
Best regards!
Best regards!
Just a quick update, I’m still woking on the amp in my spare time and slowly replacing parts. It has been confusing because the PIN numbers in the schematic are the other way around for the two ecc83’s. Technically the same but reversed. Also a few resistors have had other values compared to the schematic. Nothing way off like the first 5.1k (which was 56ohm), but still different, and quite a few resistors have wandered from their marked value. Otherwise it is going well and soon I will be able to do a light bulb test and measure some voltages. I will keep you all updated.
Cheers,
Lucas
Cheers,
Lucas
Both are exactly the same so print schematic and correct pin numbers so those match the actually used ones.
So, after a long pause (too many other projects going on) I finally got back to working on the Dynacord sv17. It is working now but I’m not there yet. Here are some measured voltages which seem a bit too high to me.
EZ81, pin 4&5 = 6.6vac
Pin 1 and Pin 7 both measure at 337vac, so together 674vac.
Between pin 3 and the first dropping resistor (5.1k) = 385vdc
After the 5.1k = 335vdc
After the 10k = 308vdc
After the 20k = 283vdc
The First ecc83 pin 1 = 146vdc
Pin 6 = 155v
The 2nd ecc83 pin 1 = 149vdc
Pin 6 =173.5v
Pin 7 = 25v
Pin 8 = 76v
Remember the pins are switched around compared to the schematic, so 1=6 and 6=1.
El84 (1) Pin 7 = 379vdc
Pin 9 = 337.5v
Pin 3 = 11,6v between 3 and 7 I measured 369v
El84(2) Pin 7 = 379,5v
Pin 9 = 337,6v
Pin 3 = 12v Between 3&7 I measured 369v
The mains here are running at about 230v but the input selector only gives me a 220v option so it might be a good idea to put a dropping resistor in front of the Input transformer.
What I have done so far;
I have replaced all Electrolytic capacitors, the second can was a 32/32 but is now a 16/16.
I replaced the first dropping resistor 5.1k
I replaced some other resistors that were off and some normal capacitors that were off.
I removed a death cap between the power switch and ground.
I replaced a broken fuse holder, changed the M1 input to a normal guitar jack and replaced all the tubes.
How is it sounding? Well it doesn’t sound bad but I’m getting some oscillations when turning the volume past half way, especially in the low frequencies, so there might be some more parts to change in the Bass and treble adjustments.
I am trying to figure out what to do with the unique filtering network.
Input 1 goes straight in to the first ecc 83 and the filtering network has no effect on it.
Input 2 also goes straight in but is effected by the filtering network.
Input 3 is filtered before and is effected by the network and has an additional signal drop when the volume knob is pulled out.
The easiest and probably most effective thing to do would be to bridge all three inputs with a 68k resistor. That way I can plug into the first input (hot) but select the second (tame)or third (tamer) and use the filtering network. Why a 68k? I read somewhere that this can reduce unwanted oscillations and besides all fenders have them.
As far as the measured voltages go, I am way above the advised limits and would like to get them down to a healthier level. Any suggestions would be appreciated! I guess a choke would be beneficial but I don’t think there is any space for one.
Many thanks,
Lucas
P.s. one thing I am concerned about is the second fuse and how this is wired up. According to online sources it is not so optimal.
EZ81, pin 4&5 = 6.6vac
Pin 1 and Pin 7 both measure at 337vac, so together 674vac.
Between pin 3 and the first dropping resistor (5.1k) = 385vdc
After the 5.1k = 335vdc
After the 10k = 308vdc
After the 20k = 283vdc
The First ecc83 pin 1 = 146vdc
Pin 6 = 155v
The 2nd ecc83 pin 1 = 149vdc
Pin 6 =173.5v
Pin 7 = 25v
Pin 8 = 76v
Remember the pins are switched around compared to the schematic, so 1=6 and 6=1.
El84 (1) Pin 7 = 379vdc
Pin 9 = 337.5v
Pin 3 = 11,6v between 3 and 7 I measured 369v
El84(2) Pin 7 = 379,5v
Pin 9 = 337,6v
Pin 3 = 12v Between 3&7 I measured 369v
The mains here are running at about 230v but the input selector only gives me a 220v option so it might be a good idea to put a dropping resistor in front of the Input transformer.
What I have done so far;
I have replaced all Electrolytic capacitors, the second can was a 32/32 but is now a 16/16.
I replaced the first dropping resistor 5.1k
I replaced some other resistors that were off and some normal capacitors that were off.
I removed a death cap between the power switch and ground.
I replaced a broken fuse holder, changed the M1 input to a normal guitar jack and replaced all the tubes.
How is it sounding? Well it doesn’t sound bad but I’m getting some oscillations when turning the volume past half way, especially in the low frequencies, so there might be some more parts to change in the Bass and treble adjustments.
I am trying to figure out what to do with the unique filtering network.
Input 1 goes straight in to the first ecc 83 and the filtering network has no effect on it.
Input 2 also goes straight in but is effected by the filtering network.
Input 3 is filtered before and is effected by the network and has an additional signal drop when the volume knob is pulled out.
The easiest and probably most effective thing to do would be to bridge all three inputs with a 68k resistor. That way I can plug into the first input (hot) but select the second (tame)or third (tamer) and use the filtering network. Why a 68k? I read somewhere that this can reduce unwanted oscillations and besides all fenders have them.
As far as the measured voltages go, I am way above the advised limits and would like to get them down to a healthier level. Any suggestions would be appreciated! I guess a choke would be beneficial but I don’t think there is any space for one.
Many thanks,
Lucas
P.s. one thing I am concerned about is the second fuse and how this is wired up. According to online sources it is not so optimal.