01-02-2019, 02:42 PM
Here's another instalment of CBL 6 works. I did consider that this thread is in the wrong forum but the work I have done on the machine may not be extensive enough to be considered a restoration, so apologies - the moderators may disagree and wish to move it.
Andy, the meter glasses were epoxied back into place as they are a close fit and the glue grips the cut edges of the glass OK.
All the valves were removed from both chassis and everything carefully cleaned. Vortexion had used mainly Mullard 'mustard' capacitors for all dry applications and Hunts electrolytics. All the smaller ones were replaced as a matter of course but I wanted to try and reform the smoothing and reservoir capacitors. There are three double 32uF cans plus one single per power supply, making seven in each channel so I was keen to try and keep them. However, after trying over the course of a couple of weeks forcing a DC potential on each separate capacitor I could not get the leakage current down to a level that I was happy with so the existing Hunts capacitors - all with 1966 date codes - were replaced. I tested the new cans and their leakage current fell to virtually zero within minutes. The Vortexion's mains transformer is a bit 'fragile' (I feel they are actually too small for the electrical load) and having lost one on another set I didn't want to chance it by putting any more stress on the HT side than was necessary.
A pair of suppression capacitors across the motor switches were replaced and those across the mains inlet plug (Hunts) were simply snipped. Just one of the interstage capacitors was replaced on each side; the signal coupler in the anode circuit of the output valve, as it has the greatest voltage stress and causes the greatest problems if it becomes leaky - passing DC through the record head.
On the mechanical side the cams and levers were cleaned and re-greased - everything was a bit dry and stiff. Switch contacts were cleaned, cams and spindles lightly oiled and greased, motor and idler bearings oiled, heads cleaned, polished and de-gaussed. The Record and Play heads are Ferrograph but the Erase head is not a type I'm familiar with.
The chassis were re-assembled and connected up ready for the first switch-on. The CBL has two mains switches, one for each side and is arranged such that the deck motors are supplied from the LH side, so only that side needs to be switched on for it to operate. So, that's where I started. As the power supplies were all re-capped I did not feel the need to run it up on my variac; just switched it straight on.
All seemed OK and the RH side was soon on as well. However, it soon became apparent that there were a few bad connections in one or more of the EF86 and ECC85 amplifier stages which were narrowed down to bad valve bases. These tiny little contacts seem to be made of chocolate - maybe corroded? I ordered some nice new ceramic bases but on disconnecting one of the originals I found that my new ones have a larger diameter and not wanting to file out a hole in a crowded chassis I elected to take one from a spare scrap chassis. Finally got it all back together and at last got it playing and recording through both channels.
Thanks for reading, that's all for now. Next I'll tackle the case..
Bill
Andy, the meter glasses were epoxied back into place as they are a close fit and the glue grips the cut edges of the glass OK.
All the valves were removed from both chassis and everything carefully cleaned. Vortexion had used mainly Mullard 'mustard' capacitors for all dry applications and Hunts electrolytics. All the smaller ones were replaced as a matter of course but I wanted to try and reform the smoothing and reservoir capacitors. There are three double 32uF cans plus one single per power supply, making seven in each channel so I was keen to try and keep them. However, after trying over the course of a couple of weeks forcing a DC potential on each separate capacitor I could not get the leakage current down to a level that I was happy with so the existing Hunts capacitors - all with 1966 date codes - were replaced. I tested the new cans and their leakage current fell to virtually zero within minutes. The Vortexion's mains transformer is a bit 'fragile' (I feel they are actually too small for the electrical load) and having lost one on another set I didn't want to chance it by putting any more stress on the HT side than was necessary.
A pair of suppression capacitors across the motor switches were replaced and those across the mains inlet plug (Hunts) were simply snipped. Just one of the interstage capacitors was replaced on each side; the signal coupler in the anode circuit of the output valve, as it has the greatest voltage stress and causes the greatest problems if it becomes leaky - passing DC through the record head.
On the mechanical side the cams and levers were cleaned and re-greased - everything was a bit dry and stiff. Switch contacts were cleaned, cams and spindles lightly oiled and greased, motor and idler bearings oiled, heads cleaned, polished and de-gaussed. The Record and Play heads are Ferrograph but the Erase head is not a type I'm familiar with.
The chassis were re-assembled and connected up ready for the first switch-on. The CBL has two mains switches, one for each side and is arranged such that the deck motors are supplied from the LH side, so only that side needs to be switched on for it to operate. So, that's where I started. As the power supplies were all re-capped I did not feel the need to run it up on my variac; just switched it straight on.
All seemed OK and the RH side was soon on as well. However, it soon became apparent that there were a few bad connections in one or more of the EF86 and ECC85 amplifier stages which were narrowed down to bad valve bases. These tiny little contacts seem to be made of chocolate - maybe corroded? I ordered some nice new ceramic bases but on disconnecting one of the originals I found that my new ones have a larger diameter and not wanting to file out a hole in a crowded chassis I elected to take one from a spare scrap chassis. Finally got it all back together and at last got it playing and recording through both channels.
Thanks for reading, that's all for now. Next I'll tackle the case..
Bill
