Hi all,
I recently bought a Grundig KS580 and am trying to restore it piece by piece. I will be posting my progress in case it helps others. [image]https://www.diyaudio.com/forums/attachment.php?attachmentid=934646&stc=1&d=1616398663[/image]. So far it looks like everything is working. Except... it looks like someone went through the amp and pulled out the tubes and output transformers. [image]https://www.diyaudio.com/forums/attachment.php?attachmentid=934647&stc=1&d=1616398663[/image]
I plan to get 2x ECC83s and 4xEL95 in place of the 2xELL80s. However, I could use help finding replacement output transformers to go with the EL95s. Here is the relevant schematic [image]https://www.diyaudio.com/forums/attachment.php?attachmentid=934639&stc=1&d=1616398230[/image]
I am new to analog electronics but here is where I am at so far:
From reading around and peaking at the datasheet, a push-pull (I think that's what the schematic is) EL95 is 10kOhm primary impedance
[image]https://www.diyaudio.com/forums/attachment.php?attachmentid=934638&stc=1&d=1616398230[/image]
Speakers are 5ohm each and, if possible, I would like to wire additional 4ohm speakers for a 2-5ohm load.
Am I correct in that this means I need 10kOhm primary and ~4Ohm secondary? Would something like a Hammond 125DSE suffice? or are there better options?
I recently bought a Grundig KS580 and am trying to restore it piece by piece. I will be posting my progress in case it helps others. [image]https://www.diyaudio.com/forums/attachment.php?attachmentid=934646&stc=1&d=1616398663[/image]. So far it looks like everything is working. Except... it looks like someone went through the amp and pulled out the tubes and output transformers. [image]https://www.diyaudio.com/forums/attachment.php?attachmentid=934647&stc=1&d=1616398663[/image]
I plan to get 2x ECC83s and 4xEL95 in place of the 2xELL80s. However, I could use help finding replacement output transformers to go with the EL95s. Here is the relevant schematic [image]https://www.diyaudio.com/forums/attachment.php?attachmentid=934639&stc=1&d=1616398230[/image]
I am new to analog electronics but here is where I am at so far:
From reading around and peaking at the datasheet, a push-pull (I think that's what the schematic is) EL95 is 10kOhm primary impedance
[image]https://www.diyaudio.com/forums/attachment.php?attachmentid=934638&stc=1&d=1616398230[/image]
Speakers are 5ohm each and, if possible, I would like to wire additional 4ohm speakers for a 2-5ohm load.
Am I correct in that this means I need 10kOhm primary and ~4Ohm secondary? Would something like a Hammond 125DSE suffice? or are there better options?
Attachments
I'm having trouble with your links, but the 4 attached pictures work fine. That's certainly a beautiful cabinet! The 4th picture shows only one transformer sized hole in the chassis. Mono?
YOS,
Chris
YOS,
Chris
Why not replace ELL80 with twin tetrode QQE03/12?
Those are cheap and easily available.
10k OPT is optimum.
4x QQE03/12 Double beam tetrode. TESLA | eBay
Those are cheap and easily available.
10k OPT is optimum.
4x QQE03/12 Double beam tetrode. TESLA | eBay
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It definitely will not do. 1st, it's a single ended item and the circuitry is push/pull. Then, the console photo shows a fairly decent record changer and an open reel tape device. Call that unit mid-FI. IMO, radio replacement grade O/P "iron" will not do. Edcor's GXPP15-10K has the mass needed, in combination with loop NFB already present, to give you good bass extension.
FWIW, I think a net speaker load of 2 Ω is a bad idea. Order 4 Ω secondary "iron" from Edcor and see to it that the net load never dips below 3 Ω.
Yes two different old manufacturers of the ELL80 put a 10Kohm input impedance for their tubes in single ended and 11Kohm impedance in push-pull.
Eli has a point when it comes to loudspeaker impedance load which is down ( mainly ) to output transformer design if someone actually studies up on this its not as simple as some think so this "2 ohm " load impedance can have negative consequences at certain frequencies .
Eli has a point when it comes to loudspeaker impedance load which is down ( mainly ) to output transformer design if someone actually studies up on this its not as simple as some think so this "2 ohm " load impedance can have negative consequences at certain frequencies .
It won't sound like an NF-10 without the original OPTs. I have an NF-1 I made into an i-pod dock a few years ago...very nice sound! The NF-1 is a similar amp to the NF-10 with a more square layout. Here's a thread I posted on another forum at the time...
Grundig Majestic Console Amp Meets i-Pod? | Audiokarma Home Audio Stereo Discussion Forums
Grundig Majestic Console Amp Meets i-Pod? | Audiokarma Home Audio Stereo Discussion Forums
Hi all. Thanks for the awesome info. I would like to get the original tubes eventually but since this is my fist vacuum tube project I want to make sure I can get things working with tubes I don't feel bad too bad exploding.
QQE03/12 seem interesting as a cheap first step but wouldn't they require changing upstream components?
[wiki=https://www.radiomuseum.org/r/grundig_nf10nf_1.html]%[/wiki]
While I am at it, should I replace all the caps? Mags's link is pretty useful regarding cap replacements. I took a closer look at the components. It looks like I am not the first one in here. Looks like someone already replaced a some of the paper caps with Mallorys.
QQE03/12 seem interesting as a cheap first step but wouldn't they require changing upstream components?
Thanks for the link. I didn't realize the mass relates to frequency response. I think I am going to go with that option. It looks like Grundig underrated the speaker since I measure 6.5Ohms DC resistance. Would the 8Ohm option be a better choice? Also, it is stereo. The second transformer is below the plate.
[wiki=https://www.radiomuseum.org/r/grundig_nf10nf_1.html]%[/wiki]
While I am at it, should I replace all the caps? Mags's link is pretty useful regarding cap replacements. I took a closer look at the components. It looks like I am not the first one in here. Looks like someone already replaced a some of the paper caps with Mallorys.
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Electrolytic caps. literally dry out over time. IMO, it is a matter of routine to replace all of the 'lytics in these "ancient" units. Hermetically sealed, Soviet surplus, K40 paper in oil (PIO) parts are excellent replacements for waxed paper signal capacitors. 716P series "Orange Drop" caps. are another possibility, but you might find the resultant sound too "bright". Jim McShane points out that a mix of dielectrics is frequently "best". That way, you listen to the amp, not the capacitors.
I see carbon composition resistors are present. Those parts have to be checked for noise and value drift. Replace out of spec. carbon comp. resistors with carbon film parts, except in grid stopper positions. Leave carbon comp. grid stoppers be!
Buy 4 Ω secondary O/P "iron". Worst case is you loose a bit of power. OTOH, a load that's too small gets you bad sound. You may have to add some sheet metal to support the Edcor "iron", given its "U" bracket mounting. I suspect that the Edcor stuff is too tall to mount on the underside.
If the bridge rectifier is selenium, it must be replaced with modern silicon parts and an adjustment made for silicon's lower forward drop. Selenium rectifiers are ticking, toxic, time bombs. 4X UF4007 diodes will be fine.
I see carbon composition resistors are present. Those parts have to be checked for noise and value drift. Replace out of spec. carbon comp. resistors with carbon film parts, except in grid stopper positions. Leave carbon comp. grid stoppers be!
Buy 4 Ω secondary O/P "iron". Worst case is you loose a bit of power. OTOH, a load that's too small gets you bad sound. You may have to add some sheet metal to support the Edcor "iron", given its "U" bracket mounting. I suspect that the Edcor stuff is too tall to mount on the underside.
If the bridge rectifier is selenium, it must be replaced with modern silicon parts and an adjustment made for silicon's lower forward drop. Selenium rectifiers are ticking, toxic, time bombs. 4X UF4007 diodes will be fine.
Not simple to adapt to a QQE.
Needs +30% heater current, lower Vg2 and at least double -Vg1.
Also needs double drive voltage, to much for the exiting phase inverter.
Mona
Replacing the ECC83 by the EF86 doesn't solve the heater over consumption, both 300mA.You could also wire the two triodes in parallel followed by the ZVN to get the big voltage swing (compared with the ELL80) to drive the QQE.
Or modify the circuit for a ECC81 (or ECC85) and hoping the transformer can cope with the 200+mA heater current.
Mona
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Oops
you are right of corse.Well, still over 100mA short.But 2x EL95 remains the more easy solution.
Mona
Is availability and cost of QQE 03/12 stock favorable? If so, add a 12 VDC "wall wart" to energize the EF86 heaters (wired in series) and use the OEM heater winding for the O/P "bottles".
A fair amount of engineering is required, no matter what, given the fact that the O/P "iron" was previously "cannibalized". AFAIK, none of the super billionaires are members here and everyone else needs to exercise at least some care with money.
A fair amount of engineering is required, no matter what, given the fact that the O/P "iron" was previously "cannibalized". AFAIK, none of the super billionaires are members here and everyone else needs to exercise at least some care with money.
We rebuilt an SE ELL80 amp from Grundig. Perhaps some inspiration.
It was a really enjoyable amp, can’t remeber who ende dup with it.
dave
It was a really enjoyable amp, can’t remeber who ende dup with it.
dave
The easiest solution would be to grab the output transformers and ECLL800 or ECLL80 tubes from a table radio chassis; stereo radios with push-pull ECLL800 or ELL80 tubes and damaged cabinet are easily available and cheap, but I guess that they are far less common in USA. If this is not a option, I would rather rebuild the amplifier as single ended with popular tubes such as EL84 or ECL86. I don't see a compelling advantage by cramming 4 scarce EL95 on that small chassis; collector value of the reworked amplifier would be negligible and the overall performance is constrained by the original speakers limitations anyway - I would be surprised if a SE EL84 amplifier with good transformers will sound any different than the original amplifier on that console.
The SE setup with "12" W. tubes idea has some merit. The $64 question is whether or not sufficient B+ current is available from the OEM power trafo.
Gain maximum flexibility by wiring the O/P tube sockets for the Russian 6Π15Π (6p15p) and regulate g2 B+ with a 0A2 gas discharge regulator. Sockets correctly wired for the 6Π15Π accept EL84s, without incident. 😉 A single 12AX7/ECC83 provides voltage amplification for both channels.
Edcor's GXSE15-5K neatly fills the O/P "iron" requirement.
Gain maximum flexibility by wiring the O/P tube sockets for the Russian 6Π15Π (6p15p) and regulate g2 B+ with a 0A2 gas discharge regulator. Sockets correctly wired for the 6Π15Π accept EL84s, without incident. 😉 A single 12AX7/ECC83 provides voltage amplification for both channels.
Edcor's GXSE15-5K neatly fills the O/P "iron" requirement.
Those Russian tubes are like the EL83, rather different from the ELL80 or EL95.
And much more heater current.
Here they have the EL95 for 4€
EL95 | PENTODE BUIS Voor 4 € HT op Electols
but rather limited stock.
They also carry the EL42 with bigger stock.Can be used to, resambles EL95, but with a rimlock socket.
The Hammond 125C OPT could be used.(evt the somewhat bigger 125D too)
Mona
And much more heater current.
Here they have the EL95 for 4€
EL95 | PENTODE BUIS Voor 4 € HT op Electols
but rather limited stock.
They also carry the EL42 with bigger stock.Can be used to, resambles EL95, but with a rimlock socket.
The Hammond 125C OPT could be used.(evt the somewhat bigger 125D too)
Mona
Thanks for the help. I will go ahead and replace caps and test the other components (Hopefully I can clean up the rats nest a bit while I am at it).
While that is cooking I will dig more into the tube situation. Most of the discussion here is over my head 😕. There are some places and people nearby I can check with that may have ELL80s, ELL80Es, or EL95s lying around or in radios on the cheap. If possible I would like to stick to the original schematic as much as possible seeing as this is my first tube project. Unless, there are substantial financial reasons otherwise.
For transformer Ill stick with 4Ohm. I don't listen at high volumes anyway.
For the rectifier Ill add a series resistor to get an appropriate drop. How close should I be to the specified output voltage? Schematic seems too specific...
While that is cooking I will dig more into the tube situation. Most of the discussion here is over my head 😕. There are some places and people nearby I can check with that may have ELL80s, ELL80Es, or EL95s lying around or in radios on the cheap. If possible I would like to stick to the original schematic as much as possible seeing as this is my first tube project. Unless, there are substantial financial reasons otherwise.
For transformer Ill stick with 4Ohm. I don't listen at high volumes anyway.
For the rectifier Ill add a series resistor to get an appropriate drop. How close should I be to the specified output voltage? Schematic seems too specific...
