Hi-Fi - Last Details

It is sweet to update this project while listening to the results. The amplifier is working really good with a warm response full of details and amazing low tones. The KT88 fits perfectly with the designed output circuit giving a pleasant result for the phono and line inputs in ultra-linear and triode configurations.

This SE system is developing around 15W in each channel and driving without problems 3-ways 100W speakers. The phono RIAA preamplifier fits the expected response curve close, but still can be improved which will be done in short.
 There is a possibility to obtain a little more of gain in the RIAA preamplifier, but in exchange for a worst SNR. The amplification taking place in this four stage circuit is noticeable and touchy to perturbancies that must be taken into account in any modification.

Some details to hit the summit, the VU circuits and the HV-Standby control circuits. Both of them to be installed in the following days.

Daily Bailiwick

What do you do when a customer brings in a fixed bias amplifier? "Release" it so different brands of tubes can be put to the ground and find your tone. In this case a Peavey Valve King came in for a power tubes replacement. Being a fixed bias amplifier forces you to buy the brand selected by the device manufacturer and still I would not trust it without checking bias.

Usually this type of modding will open a wide range of tonal possibilities. In this case it is basically a buffer-safety resistance in series with a variable one, chasis testing points and 4 matched 6L6 GC.

The original RUDY are replaced with JJs and bias adjusted to a safe level for normal power disipation and of course pure guitar tones.

Here are the 6L6 GCs ready to rock!

Another common situation is the need to take up the rains of some amps in order to deal with output volume, take advantage of it and use it as a volume-boost. It is clear you will limit the power stage punch but is always faster and cleaner than an internal modification.

Taking advantage of the effects loop can be handy to deal with this, the combination of a master volume and a true-bypass is a nice tool to overcome the problem and be able to boost parts of the piece.

Binson Echorec 2 ready for the road

A few days ago I was able to get done with the Echorec. Taking care of the pending steps, guided me to a really great session of enjoyment playing around with the Echorec.

The motor was taken apart, cleaned and rewired the cap and coils connections. That was pretty straight and let me confront the heads alignment process. This can be by far the hardest work to be done in a Binson Echorec. Being gently with the head friction while manipulating it and being able to fix it without loosing the working position is a time consuming process.

After placing the unit in its case and let it warm for a while, it was the right moment to test it for real. Expected oscillations being the best signal of the proper working of the Echorec, trimmer last adjustments even for the magic eye and time to record some files.



Nice and soft echo to play 3 Libras of APC. Forcing a little bit the echo lenght and gain we can obtain interesting effects closed to oscillating fun!

Antique radio!

A nice antique radio just arrived to be checked, repaired and restored if viable. It is a simple mono radio with volume, tuning and band selector controls.  The back plate is lost, but based in the guts I would say it was built sometime around the 40’s.

 It was a relief to see all the tubes where they are supposed to be, the rectifier UY41, the typical output pentode UL41, diode pentode UAF42, double triode UBC41 and the triode-hexode UCH42.  Although I cannot identify the model, based in the tubes and configuration we find the typical radio modules like detector, audio preamp etc

Is one of those devices designed and built when isolation from supply was not mandatory. That is why it has no power transformer and basically relies in supply voltage level and components impedance, basically five tubes, that is why this kind of radios are known as AA5. It was a way to save money in components and this design comes from the 30's. Back in those days this type radio was designed for 125Vac which is applied directly to the UY41 anode and the series connected heaters of all tubes. It is not a good idea to have a radio around, with this configuration and no back plate, it could be lethal!! Insulation trans and a back cover  is mandatory for this radio.

Components do not look too bad but already tested some of the caps and as expected they have aged, there is also some rusted nodes and degraded wires. Time to check main components and repair the unit.

Binson Echorec: Work Update!

Retaking the Binson restoration! Big steps have been taken and I hope to get done with it in a few days. Take a look at the recording unit before cleaning and properly greasing.

You can see old grease where the drum support fits to meet the internal ball gearing, the reading and recording heads, the magnets, the transmission wheel and the support for the missing spring. It took a while to clean every part, grease as needed, calibrate the spinning parts and build a new spring so the transmission wheel would have the proper friction with the magnetic drum.

The next step was reviewing the electronics and replacing wiring and components if needed. Most of resistors and caps in the signal path and tubes’ bias were replaced with quality components. I found some mods which made no sense, even some bridged resistors, as soon as I find out its purpose I will let you know the solution to this mystery.  Thankfully the wiring was not in a very bad condition which is a surprise in a Binson Echorec. One of the effects of time in this unit is some deterioration in the original LESA pots, but thankfully not enough to need replacing.

It was time to turn on the unit after all the electrical restoration included the power supply circuit. It was a good feeling to measure good readings in all the plates and bias voltages. Also checked the oscillator signal to make sure it was correct, getting a nice sinusoidal of nearly 52KHz.

It was the right moment to loose the right side plate and replace the Geloso connectors with ¼’’ female jacks. It is a good idea to use a solid support for the jacks, in this case two aluminum plates were mechanized to fit in the Binson’s plate and use new rivets to hold them in place.

I have now to rewire the front lighthning and replace the broken lamp holders, also the magic eye needs rewiring. Afterwards cleaning and adjusting the cap-motor deeply and the most consumming time operation, calibrating the recording unit. Lets speed it up!

Update of the 15W-15W Hi-Fi Tube Amp

Lack of time is what always lags behind projects. Finally, the phono preamp is nearly finished. The configuration is different from the original one, in this one 4 double triodes are used instead of the original 3. The RIAA respond is based in pasive RC filtering. The final result is much better and fitted in the RIAA curved with a clean output. The SNR and final gain are not measured jet, but it sounds as a perfect preamp for MM&MC cartridges.

I have enjoyed a little bit of  Jazz, Blues and Rock with some interesting tonal features, although as soon as it is integrated with the KT88 power stage, it will require some calibration based in owner's taste to empower the experience.

The power supply is in prototyping  process. Hope to get it ready ASAP in order to deal with the power stage.

While working in the phono preamp, some ideas for a future guitar & bass amplifier, it is in the "must do" list.

Binson Echorec 2 - Power Supply

This is a typical power supply configuration for a tube device using silicon rectifier. Transformer with several windings, rectificaction, nice reservoir, Pi filter and RC stages. Two output windings, one is a 6,3V for the heaters and the other one is basically an insulating one for the HT. The binson is based in ECC83, does not need to get to messy with HT.

Transformer was OK, passed all testing with honours, wich is always a good relief. Took out the double caps and choke to inspect & check them.

Nice Sprague caps, after 50 years amanzingly still got acceptable capacitance, but awful ESR. The choke is not in its best days but gives good readings in all the tests. If finally the Echorec is restored I will take good care of the choke, for now it will be feasible for the initial device testing.

The caps were definitely out of the game in order to obtain an acceptable ripple, even though the choke would do a good job. It is difficult-impossible to find OMC replacements and in cases like this I always like to keep the original look as much as possible. So, the only way to go was to restuff the caps with new ones. Recapping can be a hard job, but really compensates the effort when it is well done. Check out the guts of this old boy:

Nice to see how it was manufactur with that rubber band holding everything and still in place. This is its new interior:

The other double cap followed the same process. I mounted them back, reinstall the choke and replace the carbon resistors. Afterwards, I was able to do some testing to the rejuvenated power supply, with and without load, getting pretty good results.

Next step is "updating" the cap-motor. I did some previous testing and it shows some minor problems.