HI all, need some (or a lot of) help.
I have acquired a 1963 Phillips radiogram. the original turntable has been replaced (and not certain of its functioning), but the radio seems to work - with the tone, volume and balance controls still working - lovely crackly but warm am radio coming out of both channels.
My intention is to bypass the radio/ tone controls and use what is necessary of the remainder of the amplifier as a power amplifier. I will be using an existing 4 valve preamp and a set of 6 ohm (91db) speakers. Source will be a turntable and at least one line section for CD (the pre amp currently has two apart from the phono stage)
The first part I guess is to find out where I would tap into the amplifier to connect the preamp, and, then to modernise the speaker connectors.
I kind of understand how some of this kind of works.
The amplifier has 4 6GW8 tubes, with output transformers labelled with markings 12500/15 .I can see where the volume/tone control is and then where the power circuits seem to start, so I was thinking about there would be where I would tap in. Schematic attached.
It seems that the AC supply goes to the main chasie, is then split in two, being sent to power the turntable, and also to the power supply (however, it may do more than I can see).I would not be running the turntable using the existing power supply (as it currently is) - so I was thinking I could disconnect that - but not sure where.
I hope to some how use the existing controls (volume, input selector) but connect them to the FVP and avoid moving the existing amplifier (keep the 1963 asthetics - the timber cabinet with the sliding front and old controls looks groovy - but resulting in the modern and much better sound) which should not be too hard (I assume that it will just be rewiring the input selector and volume control)- but this may be a down the track stage. - and my estimation of the task may be completely wrong.
I would be interested in any inexpensive mods/ improvements that anyone can suggest. The output is rated at 7-8 W/ch, however, I have read about mono ex Hammond organ amps as guitar amps putting out 10-12W.I know I can buy a chinese amp on ebay for a few hundred bucks so I am not going overboard. DIY is satisfying but money is money.
Sorry for the long winded post.
Appreciate any help.
So to recap......
main questions are
1) where would I put the RCA's to use the existing as a power amp (and what do I do with the wires from the radio).
2) where should I disconnect the power for the turntable
3) is there anything else that can be easily disconnected to not waste electricity (ie, the AM radio and record changer for example - but I like the glow of the radio and the power light built into the cabinet) and
4) any inexpensive mods anyone could suggest to ? increase power?
thanx in advance (and I am sure that there will be more questions - sorry)
I have acquired a 1963 Phillips radiogram. the original turntable has been replaced (and not certain of its functioning), but the radio seems to work - with the tone, volume and balance controls still working - lovely crackly but warm am radio coming out of both channels.
My intention is to bypass the radio/ tone controls and use what is necessary of the remainder of the amplifier as a power amplifier. I will be using an existing 4 valve preamp and a set of 6 ohm (91db) speakers. Source will be a turntable and at least one line section for CD (the pre amp currently has two apart from the phono stage)
The first part I guess is to find out where I would tap into the amplifier to connect the preamp, and, then to modernise the speaker connectors.
I kind of understand how some of this kind of works.
The amplifier has 4 6GW8 tubes, with output transformers labelled with markings 12500/15 .I can see where the volume/tone control is and then where the power circuits seem to start, so I was thinking about there would be where I would tap in. Schematic attached.
It seems that the AC supply goes to the main chasie, is then split in two, being sent to power the turntable, and also to the power supply (however, it may do more than I can see).I would not be running the turntable using the existing power supply (as it currently is) - so I was thinking I could disconnect that - but not sure where.
I hope to some how use the existing controls (volume, input selector) but connect them to the FVP and avoid moving the existing amplifier (keep the 1963 asthetics - the timber cabinet with the sliding front and old controls looks groovy - but resulting in the modern and much better sound) which should not be too hard (I assume that it will just be rewiring the input selector and volume control)- but this may be a down the track stage. - and my estimation of the task may be completely wrong.
I would be interested in any inexpensive mods/ improvements that anyone can suggest. The output is rated at 7-8 W/ch, however, I have read about mono ex Hammond organ amps as guitar amps putting out 10-12W.I know I can buy a chinese amp on ebay for a few hundred bucks so I am not going overboard. DIY is satisfying but money is money.
Sorry for the long winded post.
Appreciate any help.
So to recap......
main questions are
1) where would I put the RCA's to use the existing as a power amp (and what do I do with the wires from the radio).
2) where should I disconnect the power for the turntable
3) is there anything else that can be easily disconnected to not waste electricity (ie, the AM radio and record changer for example - but I like the glow of the radio and the power light built into the cabinet) and
4) any inexpensive mods anyone could suggest to ? increase power?
thanx in advance (and I am sure that there will be more questions - sorry)
The speakers you plan on using are unsuitable. Look at the schematic and you will notice that 15 ohm speakers are called for. It looks like "show stopper" time.
There are no really viable mods to increase power, you'd essentially have to start over, you would have to select different output tubes, output transformers, power transformer and associated power supply components; this is not like hopping up a car.. 🙂
Eli is right, your proposed speakers are non starters with this amp due to low impedance and sensitivity.
It doesn't seem like this is the right unit to modify for your intended purpose, and shame to ruin a potentially nice vintage stereo unit.
Eli is right, your proposed speakers are non starters with this amp due to low impedance and sensitivity.
It doesn't seem like this is the right unit to modify for your intended purpose, and shame to ruin a potentially nice vintage stereo unit.
Some late '60 radiograms are a good candidate for a complete modernization, but not this one. On several high-end stereo systems of that vintage, Philips tried to reduce the output transformer distortion by using high impedence speakers and a special matched output transformer. The impedence on your speakers is a manageable 16 ohms (you can substitute each speaker with two modern 8 ohms full-range speakers wired in series). On earlier Philips stereo radios, the speakers were 600 ohms (the retrofit with a modern speaker requires a expensive special purpose 600/8 ohm Hammond transformer).
I see two way to keep your radiogram.
a) Restore the output stage and keep it as is, with the original speakers. It is not too old and you may find it surprisingly good, with a modern source (the speaker and amplifier quality is far better than the radio section). Connect your preamp output to the turntable connector on the chassis, or bypass all the controls and wire the RCA input connector for your preamplifier directy to the input of the end stage (C27 and C28 on the schematic). Check the grid capacitors; they may already be of ceramic type. If they are the older paper type you must replace them, because they may be leaking and this will damage the output tubes and the power transformer. Also replace the main filter capacitor with another one of the SAME capacity. I suggest to leave the old and possibly faulty capacitor in place to preserve the authenticity of the radio; cut the leads of the old capacitor and hide the new capacitor under the chassis. You don't need to disconnect the radio part because it draws less than 6 watts.
b) Forget the original tube amp alltogheter, remove all the tubes from the sockets and fit a small chip amp inside the radiogram, for example a TPA3116D2 based board. Power this amplifier trough the 6.3V filament supply from the original transformer. You need a voltage doubler circuit to get 12V DC, it's just a couple of cheap rectifier diodes and capacitors. The scale lamp is feed from the same 6.3v supply, so on the outside everything is the same as before.
Always make reversible modifications on well-preserved vintage equipments that has the potential to become a collector item. You may damage something that will be valuable in the future.
I see two way to keep your radiogram.
a) Restore the output stage and keep it as is, with the original speakers. It is not too old and you may find it surprisingly good, with a modern source (the speaker and amplifier quality is far better than the radio section). Connect your preamp output to the turntable connector on the chassis, or bypass all the controls and wire the RCA input connector for your preamplifier directy to the input of the end stage (C27 and C28 on the schematic). Check the grid capacitors; they may already be of ceramic type. If they are the older paper type you must replace them, because they may be leaking and this will damage the output tubes and the power transformer. Also replace the main filter capacitor with another one of the SAME capacity. I suggest to leave the old and possibly faulty capacitor in place to preserve the authenticity of the radio; cut the leads of the old capacitor and hide the new capacitor under the chassis. You don't need to disconnect the radio part because it draws less than 6 watts.
b) Forget the original tube amp alltogheter, remove all the tubes from the sockets and fit a small chip amp inside the radiogram, for example a TPA3116D2 based board. Power this amplifier trough the 6.3V filament supply from the original transformer. You need a voltage doubler circuit to get 12V DC, it's just a couple of cheap rectifier diodes and capacitors. The scale lamp is feed from the same 6.3v supply, so on the outside everything is the same as before.
Always make reversible modifications on well-preserved vintage equipments that has the potential to become a collector item. You may damage something that will be valuable in the future.
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Thanx for that Eli - shows I should go to the childrens section of the valve amplifier library and do some basic reading.
But another question if I may (the library is closed at the moment - and off to see starwars),
I came across an article for Heathkit AA-32 Stereo Amplifier.
It seems to use the same power tubes as I have (6GW8) but the output transformer has outputs of 4, 8 and 16 ohm. Would replacing the output transformers with variable outputs overcome my problem and allow me to use my existing speakers?
appreciate your assistance.
Thanx for that kevinkr. looks like I should see how it all sounds before I want to fix it.
appreciate your assistance.
Thanx Pcan.
I like your first suggestion - keep as is, tap into the power stage and use existing pre amp. When it comes to replacing the capacitors, I am not sure of the ones you are describing.
The schematic identifies the ones that are paper, and should I replace all of them? also, could you describe (from the schematics) the grid and main filter capacitors.
appreciate your assistance.
The B+ filter capacitors are C44-C45-C46 (50-50-8 uF 350V), they are usually combined in a single capacitor block. Replace them with modern discrete 450V 47-47-10 uF.
The grid capacitors are C30-C31-C32-C33-C34-C35. Use modern ceramic disk (round and usually reddish), or polyester 1000V (the bright yellow ones).
Replace the cathode bypass capacitors (C38 and C39) with 25uF 63V. You may try 10uF instaead 25uF, this will lower slightly the amplifier gain and distortion.
While working near the audio tube sockets, DO NOT change the position of any wire or component. Tube amplifier circuits are high impedence and they may self-oscillate due stray capacitances. This amplifier seems to be prone to this malfunction, since Philips put several capacitors and resistors for this exact purpose. As others already noticed, this is a oddball, purpose-built amplifier and I would try to avoid any unnecessary change such as output transformer surgery. I've seen far better amplifiers on German and USA radiograms. On the plus side, after the restore it may have a lovely sound. I have several Philips radio on my collection and the sound is nice, usually.
The grid capacitors are C30-C31-C32-C33-C34-C35. Use modern ceramic disk (round and usually reddish), or polyester 1000V (the bright yellow ones).
Replace the cathode bypass capacitors (C38 and C39) with 25uF 63V. You may try 10uF instaead 25uF, this will lower slightly the amplifier gain and distortion.
While working near the audio tube sockets, DO NOT change the position of any wire or component. Tube amplifier circuits are high impedence and they may self-oscillate due stray capacitances. This amplifier seems to be prone to this malfunction, since Philips put several capacitors and resistors for this exact purpose. As others already noticed, this is a oddball, purpose-built amplifier and I would try to avoid any unnecessary change such as output transformer surgery. I've seen far better amplifiers on German and USA radiograms. On the plus side, after the restore it may have a lovely sound. I have several Philips radio on my collection and the sound is nice, usually.
Time out, please! The 6GW8/ECL86 is out of production and NOS is scarce. The 91 dB. (if that claim is accurate) sensitive speakers require upwards of 16 WPC. You can't get the power you need by tweaking the console.
Money will have to be spent. TANSTAAFL. Either more sensitive speakers acquired (build or buy) or more amplifier power acquired.
FWIW, you can check the archives for recent activity, where I've been helping a Hungarian named Sebastian with an "El Cheapo Grande". That sort of amp has the "stones" the 91 dB. speakers require.
Money will have to be spent. TANSTAAFL. Either more sensitive speakers acquired (build or buy) or more amplifier power acquired.
FWIW, you can check the archives for recent activity, where I've been helping a Hungarian named Sebastian with an "El Cheapo Grande". That sort of amp has the "stones" the 91 dB. speakers require.
Eli, I totally agree with you that connecting the 91db speakers to this vintage Philips amplifiere will not work. The only cheap option now is to buy a bunch of capacitors to restore the circuit at factory specifications and evaluate the sound quality with the stock radiogram speakers. I believe that a preliminary judgement could be done replacing the electrolytic capacitors only and soldering the RCA inputs after the volume control, this will cost only a few dollars and 2 hours time if the general device condition is sound.
ECL86 tubes aren't rare at this point in time; this tube and the PCL86 version were the default output tube of b&W european TVs, there are truckloads of good tube pulls still available and NOS tubes are easy to get (yet). But you are right; no complete hi-fi sound will ever come out from this amplifier made with weak television tubes. Any serious investment of time or money is better spent elsewere, as you said. Nevertheless, if jag142 will like the sound of the restored amp, a separate active subwoofer could change the scenario. 7W (more realistically: 5w, because Philips output transformers were tiny) may eventually be enough for the medium-high section.
By the way, the Mullard/Philips reference design for the ECL86 push-pull is the "Ten Watt High Quality Stereophonic Amplifier" published in 1962 Ten Watt High Quality Stereophonic Amplifier and this Philips amplifier is a cost-reduced, mutilated version. The designers removed the ultralinear tap from the transformer and put the cathode bypass in common between the two tubes, so if one of them fails, the other will follow. Of course they also removed the expensive EF86 preamplifier and cranked up the gain of the pentode to the ceiling. Hardly a hi-fi choice by modern standards, but some people like this sound.
ECL86 tubes aren't rare at this point in time; this tube and the PCL86 version were the default output tube of b&W european TVs, there are truckloads of good tube pulls still available and NOS tubes are easy to get (yet). But you are right; no complete hi-fi sound will ever come out from this amplifier made with weak television tubes. Any serious investment of time or money is better spent elsewere, as you said. Nevertheless, if jag142 will like the sound of the restored amp, a separate active subwoofer could change the scenario. 7W (more realistically: 5w, because Philips output transformers were tiny) may eventually be enough for the medium-high section.
By the way, the Mullard/Philips reference design for the ECL86 push-pull is the "Ten Watt High Quality Stereophonic Amplifier" published in 1962 Ten Watt High Quality Stereophonic Amplifier and this Philips amplifier is a cost-reduced, mutilated version. The designers removed the ultralinear tap from the transformer and put the cathode bypass in common between the two tubes, so if one of them fails, the other will follow. Of course they also removed the expensive EF86 preamplifier and cranked up the gain of the pentode to the ceiling. Hardly a hi-fi choice by modern standards, but some people like this sound.
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